In Saint Thomas Aquinas’ treatise on the Sacrament of the Eucharist in the Tertia Pars of his Summa Theologiae, he says that the “whole Christ”  is “really present”  in the Eucharist. For Thomas, this means that “Christ Himself is contained in the Eucharist sacramentally”  as the Son of God, not “in His proper species” , but “under the sacramental species” . In this sense, He is present in the Eucharist, not as He appears in the proper species of His Glorified Humanity in Heaven , but as He appears under “the species of bread and wine” . For this reason, He is in this sacrament “in a special manner” . Accordingly, this special presence of Christ in the Eucharist is “proper to this sacrament” alone . For He is really and fully contained in the Eucharist sacramentally as the “God-Man” . Indeed, He remains the Second Person of the Blessed Trinity, the Incarnate Son of God, under the species of this sacrament. Hence, this is a real or true presence of Christ in this sacrament.
According to Thomas, the basis for this teaching is the authority of the Divine Person of Christ Himself . During the Last Supper Christ revealed to His Apostles His real presence in the Eucharist . In Thomas’ teaching, this means that Christ is really contained in the Eucharist as the God-Man “after the manner of substance” . Thus, His real presence in the sacrament is a substantial presence. The term substance (substantiae) here from the Latin “substare” signifies the unchangeable, substantial reality of a thing, what the thing really is in itself substantially as it stands under changeable appearances or sensible accidents. For instance, the substance of what a person is, what he really is substantially remains unchanged and unchangeable, inasmuch as he remains a human being in the substance of his human nature, but his sensible appearance certainly can and will change as he matures physically and ages from infancy to childhood, from childhood to adolescence, from adolescence to adulthood, and from adulthood to an elderly person. Throughout these changes in his appearance, he remains the same substantially in his human nature. His appearance may also change due to injury, illness, or surgery, but he remains fully what God created him to be, a human being in the substance of his humanity. As a result, Thomas says that Christ remains unchanged and unchangeable in what He really is substantially in the substance of His Humanity, the God-Man, under the appearance of the sacramental species . Thus, for Thomas, Christ is “substantially present”  in the Eucharist. The sacramental species here includes the signs of bread and wine that contain Christ substantially. For at the Last Supper Christ proclaimed to His apostles His real, substantial presence in the Eucharist, the presence of His Body and Blood, under the appearance of the sacramental signs of bread and wine. According to the Gospel, first, “he took the bread, said the blessing, broke it and gave it to [His Apostles], saying, ‘This is my body’…And [then] the cup [of wine]…saying, ‘This…[is] my blood’” . By these words Christ revealed to His apostles His real, substantial presence in the Eucharist through the signs of bread and wine. For this reason, He wills for these sacramental signs to contain the reality they signify. The reality contained here is the real presence of the Body and Blood of the God-Man, Jesus Christ, under the appearance of bread and wine that signify Christ. Accordingly, Thomas teaches that at the Last Supper Christ Himself instituted the Eucharist as both sign and reality. For there Christ proclaimed that He really becomes fully present substantially  in His Body and Blood through sacramental signs .
Specifically, in his treatise, Thomas says that the “whole Christ” is “really present” in the Eucharist “in a twofold manner” . In the first place, he says that Christ is present in the Eucharist “by the power of the sacrament [itself]” . This power refers to the “efficacy”  of Christ’s “words of consecration”  through the action of the Holy Spirit. These are the “words for consecrating the bread and wine”  that Christ “the High Priest”  pronounced “in instituting [the Eucharist]”  as the “memorial of [His] Passion”  during the Last Supper. In doing so, He instructed His Apostles to henceforth commemorate this sacrificial offering of Himself, the offering of His Body and Blood on the cross, through their consecration of the bread and wine in the Eucharist . For this reason, He says to them, “Do this in remembrance of me” . As such, Thomas says that Christ conferred upon His Apostles a participation in his priestly ministry  during His institution of the Eucharist at the Last Supper . The oldest scriptural account of this institution is recorded in Saint Paul’s First Letter to the Corinthians. In this letter Paul reminds them: “For I received from the Lord what I also handed on to you, that the Lord Jesus, on the night he was handed over, took bread, and, after he had given thanks, broke it and said, ‘This is my body that is for you. Do this in remembrance of me.’ In the same way also the cup, after supper, saying, ‘This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me.’ For as often as you eat this bread and drink this cup, you proclaim the death of the Lord until he comes” . As the first priests of the Church who received their priesthood from Christ, the Apostles, in their faithfulness to what Christ Himself had instructed them to do, would be the first to proclaim “the death of the Lord” in the Eucharist as they acted in the person of Christ the Head (in persona Christi capitis) by proclaiming the words of consecration over the bread and wine and consuming them for what they really had become in this consecration, the true Body and Blood of Christ. Accordingly, this would be a proclamation of the sacrifice of Christ that all priests after them would be called to proclaim. In Thomas’ teaching, as the priest pronounces the words of consecration from Christ’s institution of the Eucharist at the Last Supper, there is a substantial change that occurs in the substance of the Eucharistic species through the power of the sacrament. This means the Eucharistic bread and wine are substantially changed in this consecration. This change that occurs in the consecration at Mass is sui generis (a singular class in itself). As a consequence, the substantial change here does not conform to the categories of Aristotle, who believed that every substantial change required a change in appearance or what he called the accidents. As such, in this special or supernatural substantial change in the consecration of the bread and wine, Christ becomes present substantially, but the appearance of bread and wine remain unchanged. Thomas calls this substantial change, transubstantiation, for here the substance of bread and wine are changed substantially into the substance of Christ through the priest’s pronouncement of the words of consecration. Consequently, in this sacred priestly act, the substance of the bread and wine cease to be. For as the priest pronounces the words of consecration the full substance of the bread really becomes the full substance of the Body of Christ, and the full substance of the wine really becomes the full substance of the Blood of Christ. In this sense, the Body and Blood of Christ really and fully become present in the Eucharist “after the manner of substance”. This means that the full substance of the Body and Blood of Christ is truly and fully present under each of the Eucharistic species of bread and wine, including under every part, meaning under every piece and drop of the species . On this basis, after the consecration, the Body and Blood of Christ really and fully become present substantially under the appearance of bread and wine by the power of the sacrament. This is the first manner of Christ’s real presence in the Eucharist.
Secondly, Thomas also says that Christ is really present in the Eucharist from natural or real concomitance. This is the second manner of the real presence of Christ in the Eucharist. Specifically, this means that although the substantial change or transubstantiation of the substance of the Eucharistic bread terminates in the substance of the Body of Christ, the full Human Nature and Divinity of Christ are also present in the Body of Christ by their union in Him from real concomitance. In this sense, the Blood, Soul and Divinity of Christ are present concomitantly in the Body of Christ. Hence, the recipient of the Body of Christ receives Christ fully. The same is true of the Blood of Christ. As the substantial change of the wine terminates in the substance of the Blood of Christ, the full Humanity and Divine Nature of Christ are also present in His Blood concomitantly by reason of their union in Him. Accordingly, the Body, Soul and Divinity of Christ are fully present in the Blood of Christ. In receiving the Blood of Christ, the communicant receives Christ fully. As such, the term “concomitance” refers to the real, indissoluble unity or relation of the full Humanity and Divinity in the single Subject or Person of Christ Himself by His incarnation. From the time of His conception as man in the All Holy Virgin through the Holy Spirit, these Natures, the Human and the Divine, have been fully and perfectly united in Him. For this reason, in the priest’s consecration of the Eucharistic species of bread and wine, these Natures remain fully and perfectly united in Christ in every piece and in every drop of the Eucharist. On this basis, the full Person of Christ, the God-Man, is really present in the Eucharist in His Body, Blood, Soul and Divinity through the “power of the sacrament” and by “real concomitance” .
According to Thomas, Christ first and foremost becomes fully present substantially in the Eucharist as a means to efficaciously communicate the grace of the saving merits of His satisfactory Passion, His suffering and death on the cross, to human beings. As such, Thomas says that the reason Christ, the Uncreated Son of God from all eternity, became the Son of Man through a created Human Nature was to mercifully offer Himself fully to the Father through the Holy Spirit as a Sacrifice to satisfy for the original sin of Adam and Eve and for all particular sins of their descendants. For they had acted against the order of God’s justice through sin. Consequently, God’s justice required satisfaction for sin. In treating the doctrine of satisfaction, Thomas recalls the general principle that a human being can satisfy for a particular brother or sister if he remains in a state of charity, but he cannot satisfy for all human beings because the act of a single human being does not have the value of all the people in the human race . On the other hand, the action of Christ, the Divine Person of God the Son as Man had a value that could satisfy for the sin of all people by reason of His Infinite Dignity . In Thomas’ teaching, he defines satisfaction as every difficult action or passion by a person that removes some impediment or impairment to the fulfillment of glory. In the case of Christ, He satisfied for the sins of the human race by offering Himself as the Lamb of Sacrifice. In doing so, He suffered in His Human Nature to pay the debt of punishment that human beings incurred for sinning against God’s justice, but Thomas says that the suffering of Christ alone could not satisfy for their sin. The suffering was not the principle or cause of satisfaction. On the contrary, the principle of satisfaction was the love in the heart of Christ as a habit of His soul, whereby He was inclined as Man to voluntarily satisfy for human beings . For this reason, Friar Romanus Cessario, O.P., says that the efficacy of Christ’s satisfaction for sin was in His love . As a result, in offering Himself in His Body and Blood on the cross as a sacrificial act of love, He efficaciously merited the glory of salvation for all human beings. This is what reconciled them to God in preparation for the glory of Heaven and the glorious resurrection.
For Thomas, Christ the High Priest constituted the Apostles as the first priests of the Church at the Last Supper to participate in His priestly ministry by dispensing the grace of the saving merits of His Passion through the Sacraments He instituted in the Church. Hence, all the Sacraments have their relevance here, but especially the Eucharist in this article. For in the Eucharist the sacrificial offering of Christ on the cross in His Body and Blood, once and for all in human history, is really made present substantially on the altar daily through the priest’s pronouncement of the words of consecration . Thus, Thomas says that the offering of the Eucharist is, first of all, called a Sacrifice because it images the offering of Christ as the Sacrificial Lamb on the cross . In this sense, here the offering of the Eucharist is an image representing the offering of Christ in His Passion. In the second place, Thomas teaches that the Eucharist is also called a Sacrifice because a person receives a spiritual participation in the Passion of Christ through particular sacrificial effects or fruits in the Eucharist. As a Sacrifice, the Eucharist can be offered for the spiritual benefit of any person, present or absent from the Holy Sacrifice of the Mass, including for the dead . On this basis, the priest offers the Sacrifice of the Eucharist for the people of God that they may participate more and more in the fruits of the Passion of Christ.
Moreover, Thomas teaches that the Eucharist is a Sacrament because in Holy Mass the people of God receive the Body and Blood of Christ. Here the sacramental effects benefit only the people who are present to consume them . In receiving Christ in First Holy Communion, a person receives the Bread from Heaven, the Heavenly Manna, as the spiritual nourishment he requires to be fully alive as image of Christ. For in Baptism the person was recreated in the image of Christ through the grace of justification that he may live for Him as a faithful disciple. As such, this grace perfected his nature for the reception of Christ in Holy Communion throughout his life. In doing so, he receives various fruits or effects. In particular, Christ tells His disciples that this fullness of life for them through Holy Communion includes the spiritual or interior presence of the life of Christ in their hearts, eternal life and the glorious resurrection on the Last Day . Furthermore, as people who are called to be fully alive in Christ, they can only reach full maturity or perfection in Christ through their regular reception of the Eucharist. This Bread of Life will help them live and act faithfully as disciples of Christ.
All the same, a person considering the Eucharist, especially a non-Catholic or a Catholic not fully formed in Church teaching, may reasonably question if this doctrine is really true. After all, as a creature created in God’s divine image, the human being is a rational, free person who has a natural desire to learn the truth available to him through his spiritual, bodily nature. For this reason, he fulfills himself as man intellectually by forming a true understanding of the objects that he perceives through the senses of his body. This formation in truth for the human being will certainly involve questioning the true nature or meaning of such objects. He will especially question those difficult teachings or claims about particular objects that do not seem to be based on the reality he perceives through his bodily senses. In his mind, these teachings would include the doctrine of Christ’s real presence in the Eucharist. As such, he readily questions this doctrine. For he does not naturally sense the Son of God as man under the Eucharistic species. Indeed, in this sacrament he does not sense Christ as he senses other sensible goods or objects in creation. On the contrary, he merely perceives the bread and wine in the Eucharist. Consequently, he may reasonably ask, “Is this doctrine really credible or true? Is Christ’s Body and Blood really present substantially in the Eucharist?” Is He really contained as the God-Man under the Eucharistic species? Certainly, the mature Catholic formed in Church teaching is fully prepared to say “yes” to this question. He is ready to profess the real presence of Christ in the Eucharist. For he has reached a certain maturity in Christ as a Catholic. On the other hand, the non-Catholic or the Catholic unformed doctrinally is unprepared to say “yes” to this teaching. As a result, he will question the real presence of Christ under the Eucharistic species. Indeed, he may either doubt or reject this doctrine. In a sense, either response seems reasonable for such a person. For in the Eucharist Christ does not appear as He is in His proper species as the God-Man in Heavenly Glory. Hence, a person questioning this doctrine seems to have good reason for doubting or rejecting the real, substantial presence of Christ. After all, the sensible signs of bread and wine do not have the natural sensible form or appearance of a person. This means they do not image the Person of Christ accidentally in His proper species as He is in Heaven. For the sensible accidents of the Eucharistic species, including height, width, weight, shape, color, scent and flavor, do not belong to the nature of a person. On the contrary, they belong to the nature of bread and wine. Consequently, the human being merely senses them accidentally as bread and wine through his sense nature. Indeed, he sees, touches, tastes and smells them as such. In doing so, he perceives them, not for what they “really are” substantially, but for what they “appear to be” accidentally. Accordingly, he identifies merely their accidental sense nature through the natural operations of his bodily senses. For the proper or natural objects of his sense organs include all the sensibles in material creation, not the real substance of Christ in the Eucharist. Therefore, the real, substantial presence of Christ in this Sacrament is not subject to the senses of the body. These organs do not have the capacity to sense Christ as such. On this basis, created in the image of God, the non-Catholic or unformed Catholic, in his desire for truth will readily question the real presence of Christ in the Eucharist, after perceiving merely the sensible signs of bread and wine.
As the image of God, this questioning can help such a person open his mind to receive the truth he desires, but this alone is insufficient for fulfilling the end. He will require more than merely questions to fulfill his desire for truth. First of all, as a rational being, he will need intellectual formation in the truth of the Church’s teaching concerning the Sacrament of Eucharist. This formation will help him understand what the Church is proclaiming in this doctrine materially. In this education, he will learn that the Church’s doctrine of the real, substantial presence of Christ in the Eucharist completely transcends all the natural faculties and operations of man. This would include not only the natural operations of his bodily senses as already mentioned, but also the natural reasoning capacity of his mind or intellect. Consequently, he cannot naturally reason from the sensible signs of the Eucharistic species to the conclusion that Christ is really present substantially in the Eucharist. For in this Sacrament the truth of the real, substantial presence of Christ is not naturally subject or accessible to the natural operations or faculties of man. Accordingly, the non-Catholic or unformed Catholic will first have to develop at least a sufficient understanding of the Catholic doctrine of the Eucharist materially in preparation to formally receive this truth. This formation in truth will be the first means of preparing himself for the desired end.
Secondly, his preparation will also involve opening his heart to the grace of God. According to Thomas, God’s grace perfects the nature of man supernaturally. On the one hand, for the non-Christian, this movement to perfection in him begins through an actual grace he receives from God. This particular grace is a temporary supernatural illumination or inspiration that moves the person to open himself to receive the habitual grace of justification in Baptism. On the other hand, for the unformed Catholic, a person who has not practiced Catholic faith and morals during his life, the movement to perfection in him also begins through an actual grace he receives from God, but this grace moves him to open his heart to the Sacrament of Penance (Confession). For in this Sacrament he will, once again, receive the grace of justification he lost sometime after Baptism. Thus, in either case, the human nature of the non-Christian or the unformed Catholic will be perfected supernaturally through the grace of justification in Baptism or Confession. In particular, Thomas teaches that in the Sacrament of Baptism God perfects the mind of the human being supernaturally through the theological virtue of faith  that he may “see” the God-Man “substantially” under the Eucharistic species by an intellectual act of faith. As for the unformed Catholic, the grace of the Sacrament of Penance perfects his mind supernaturally through faith that he may also “see” the real, substantial presence of Christ in the Eucharist. In this sense, for the human being, “seeing Christ” is a metaphor for believing in the real, substantial presence of Christ intellectually through faith. For “the substance” of Christ in the Eucharist comes “under the intellect”  as the proper object of the mind that has been supernaturally perfected by faith . This means that the real, substantial presence of Christ only becomes subject or accessible to the person in the supernatural perfection of his intellect through faith. Thus, Thomas says that the human being is perfected in his mind through theological faith that he may believe that Christ is really present substantially under the appearance of the sensible signs or accidents of bread and wine . Therefore, he becomes capable of a supernatural act of the intellect to believe through the faith he receives in the grace of justification. On this basis, this grace of God perfects the nature of man that he may formally believe in the truth contained in the Eucharist.
At the same time, the Church teaches that in Baptism and Penance the beneficiary of the Sacrament is initially perfected in his intellect through theological faith merely in seminal or seed form. In this sense, the faith here is not a fully perfected faith, but merely the beginning of the seed of faith in the intellect that still requires maturation . Thus, Friar Romanus Cessario, O.P., says that for a person who has formally professed his faith in Christ, either through Baptism or Penance, there is still in him a certain movement to perfection of faith that remains incomplete, inasmuch as he remains in potency to full perfection or conformity to Christ as a graced human being . This seminal faith in the person is certainly sufficient for seeing Christ in the Eucharist, but as the person matures in his bodily and spiritual nature as man through childhood, adolescence and adulthood, he cannot remain unchanged or underdeveloped intellectually as a person of faith. For God did not first create him and later recreate him merely to remain immature as a believer. On the contrary, God wills for the person to gradually develop to adulthood in his faith. According to Cessario, the Christian can only mature if he remains spiritually alive in Christ. Hence, this maturation indicates that he is in the grace of Christ . For this reason, in the Gospels Jesus instructs his disciples to become perfect as sons of God . Indeed, he uses certain metaphors from creation, agriculture and commerce in his parables to call them to increase or develop the seeds of grace they have received from God interiorly. The Church teaches that this would certainly include the seminal gifts and virtues they have received from God in Baptism and Penance such as faith. Accordingly, as they develop these seeds of grace as faithful disciples, they will more and more bear fruit, first and foremost, in their hearts through the intellectual act of faith . In fact, in his preaching St. Paul calls Christians to this faithful maturation in Christ . He also reminds them that God alone will “cause” this fruitful increase or maturation in them . He alone will fully perfect them as a people of faith. All the same, this does not mean that they cannot contribute to their maturation. Certainly, they can. As persons created in the image of God, and recreated in the image of Christ, through the grace of justification, these people have the graced, rational capacity for the theological and moral actions that will dispose or prepare them to receive from God an increase of faith in Christ. In particular, they can till the soil of their hearts, nurture their seeds of faith and water them through prayer, study and contemplation of truth, penitential sacrifice and acts of mercy. In Thomas’ teaching, this is a living faith for them, a maturing faith informed by love. For this reason, through such faith, they become more and more perfected in their love for the real, substantial presence of Christ under the Eucharistic species. This faithful love for Christ in the Eucharist is at the heart of their movement to full conformity to the person of Christ in this life. Consequently, seminal faith is certainly sufficient for beginning this pilgrimage of faith in Christ, but does not suffice for full perfection in Christ. The disciple can only become fully conformed to Christ through the perfection of his faithful love for the real, substantial presence of Christ in the Eucharist. This perfection requires his maturation as a man of faith throughout his life to the desired end or terminus. As a result, the grace of God further perfects the nature of man as he matures to full adulthood as a faithful lover of Christ. In doing so, he comes to see the real substance of the Person of Christ, the God-man, under the Eucharistic species more and more fully through the eyes of a loving and maturing faith.
In the Crucified and Risen Christ with Blessed Mary,
Friar Mariano D. Veliz, O.P.
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Pope Pius V. Catechism of the Council of Trent. Charlotte, North Carolina: Tan
 Summa Theologiae, IIIa, Q. 76, a. 1-2.
 Ibid., Q. 75, a. 2.
 Ibid., Q. 73, a. 5, Q. 80, a. 5.
 Ibid., Q. 80, a. 5.
 Ibid., Q. 76, a. 8, Q. 90, a. 2.
 Ibid., Q. 77, a. 1, Q. 80, a. 2.
 Ibid., Q. 75, a. 1.
 Ibid., Q. 36, a. 5.
 Ibid., Q. 75, a. 1.
 Ibid., Q. 73, a. 5.
 Ibid., Q. 76, a. 4.
 Ibid., a. 7.
 Luke 22:19-20.
 Idem, Summa Theologaie, IIIa, Q. 78, a. 6.
 Knowing the Love of Christ, Pg. 114.
 Idem, Q. 76, a. 1.
 Ibid., Q. 78, a. 4.
 Ibid., Q. 83, a. 1.
 Ibid., Q. 78, a. 6.
 Ibid., Q. 83, a. 6.
 Ibid., Q. 74, a. 5.
 Ibid., Q. 76, a. 2.
 Ibid., Q. 83, a. 2, Q. 82, a. 1-2.
 1 Corinthians 11:24-26.
 Idem, Q. 63, a. 3, Q. 82, a. 3.
 Ibid., Q. 82, a. 2.
 1 Corinthians 11:23-26
 The Council of Trent, Session XIII, Canon III.
 Idem, IIIa, Q. 76, a. 1.
 De Veritate, Q. 29, a. 7.
 Ibid., Q. 29, a. 3 and 7.
 Ibid., Q. 29, a. 4, Summa Theologiae, IIIa, Q. 14, a. 1.
 The Godly Image, Chapter IV, Pg. 93.
 Idem, Summa Theologiae, IIIa, Q. 83, a. 1.
 Ibid., IIIa, Q. 83, a. 1, Q. 79, a. 5.
 Ibid., IIIa, Q. 83, a. 1, Q. 79, a. 7.
 Rediscovering Aquinas and the Sacraments, Chapter 4, Pg. 40.
 John 6: 53-58.
 Idem, Summa Theologaie, IIa-IIae Q. 1, a. 1 and 3.
 Ibid., IIIa, Q. 76, a. 7.
 The Catechism of the Catholic Church: 1253.
 The Moral Virtues and Theological Ethics, Chapter 1. The Moral Virtues and Christian Faith, Pg. 24.
 Ibid., Pg. 25.
 Matthew 5:48.
 Mark 4:1-20, 4:26-34, Luke 19:11-26 and John 15:1-8.
 Ephesians 4:13-16; Philippians 1:25, 3:9, 12, 15; 1 Corinthians 2:6, 14:20; Colossians 1:6, 9-10; Romans 6:5; and 1 Thessalonians 4:10.
 1 Corinthians 3:6-7 and Colossians 2:19.