Christ on a certain occasion discoursing with the Jews said, Except ye eat My flesh and drink My blood, you have no life in you. They not having heard His saying in a spiritual sense were offended, and went back, supposing that He was inviting them to eat flesh.

In the Old Testament also there was show-bread; but this, as it belonged to the Old Testament, has come to an end; but in the New Testament there is Bread of heaven, and a Cup of salvation, sanctifying soul and body; for as the Bread corresponds to our body, so is the Word appropriate to our soul. — Catechetical Lecture 22.

He once in Cana of Galilee, turned the water into wine, akin to blood, and is it incredible that He should have turned wine into blood? When called to a bodily marriage, He miraculously wrought that wonderful work; and on the children of the bride-chamber, shall He not much rather be acknowledged to have bestowed the fruition of His Body and Blood?

Wherefore with full assurance let us partake as of the Body and Blood of Christ: for in the figure of Bread is given to you His Body, and in the figure of Wine His Blood; that you by partaking of the Body and Blood of Christ, may be made of the same body and the same blood with Him. For thus we come to bear Christ in us, because His Body and Blood are distributed through our members; thus it is that, according to the blessed Peter, we become partakers of the divine nature. — Catechetical Lecture 22.

I received of the Lord that which also I delivered unto you, how that the Lord Jesus, in the night in which He was betrayed, took bread, &c.

Even of itself the teaching of the Blessed Paul is sufficient to give you a full assurance concerning those Divine Mysteries, of which having been deemed worthy, you are become of the same body and blood with Christ. For you have just heard him say distinctly, That our Lord Jesus Christ in the night in which He was betrayed, took bread, and when He had given thanks He broke it, and gave to His disciples, saying, Take, eat, this is My Body: and having taken the cup and given thanks, He said, Take, drink, this is My Blood . Since then He Himself declared and said of the Bread, This is My Body, who shall dare to doubt any longer? And since He has Himself affirmed and said, This is My Blood, who shall ever hesitate, saying, that it is not His blood? — Catechetical Lecture 22.

After this ye hear the chanter inviting you with a sacred melody to the communion of the Holy Mysteries, and saying, O taste and see that the Lord is good . Trust not the judgment to your bodily palate no, but to faith unfaltering; for they who taste are bidden to taste, not bread and wine, but the anti-typical Body and Blood of Christ. — Catechetical Lecture 23.

One ought, moreover, to recognise that it is one thing to look at a matter as it is, and another thing to look at it in the light of reason and thought. In the case of all created things, the distinction of the subsistences is observed in actual fact. For in actual fact Peter is seen to be separate from Paul. But the community and connection and unity are apprehended by reason and thought. For it is by the mind that we perceive that Peter and Paul are of the same nature and have one common nature. For both are living creatures, rational and mortal: and both are flesh, endowed with the spirit of reason and understanding. It is, then, by reason that this community of nature is observed. For here indeed the subsistences do not exist one within the other. But each privately and individually, that is to say, in itself, stands quite separate, having very many points that divide it from the other. For they are both separated in space and differ in time, and are divided in thought, and power, and shape, or form, and habit, and temperament and dignity, and pursuits, and all differentiating properties, but above all, in the fact that they do not dwell in one another but are separated. Hence it comes that we can speak of two, three, or many men.

And this may be perceived throughout the whole of creation, but in the case of the holy and superessential and incomprehensible Trinity, far removed from everything, it is quite the reverse. For there the community and unity are observed in fact, through the co-eternity of the subsistences, and through their having the same essence and energy and will and concord of mind, and then being identical in authority and power and goodness —” I do not say similar but identical —” and then movement by one impulse. For there is one essence, one goodness, one power, one will, one energy, one authority, one and the same, I repeat, not three resembling each other. But the three subsistences have one and the same movement. For each one of them is related as closely to the other as to itself: that is to say that the Father, the Son, and the Holy Spirit are one in all respects, save those of not being begotten, of birth and of procession. But it is by thought that the difference is perceived . For we recognise one God: but only in the attributes of Fatherhood, Sonship, and Procession, both in respect of cause and effect and perfection of subsistence, that is, manner of existence, do we perceive difference . For with reference to the uncircumscribed Deity we cannot speak of separation in space, as we can in our own case. For the subsistences dwell in one another, in no wise confused but cleaving together, according to the word of the Lord, I am in the father, and the father in Me: nor can one admit difference in will or judgment or energy or power or anything else whatsoever which may produce actual and absolute separation in our case. Wherefore we do not speak of three Gods, the Father, the Son, and the Holy Spirit, but rather of one God, the holy Trinity — Book I, Chapter 8, Concerning the Holy Trinity.