Ephesians 5:30

Just as Eve was fashioned from Adam, so were we from Christ the Lord. We are buried with him in baptism. We rise with him. We eat his body and drink his blood [in the Eucharist].

"Because we are members of His body, of His flesh and of His bones." Tell me not that such and such things are so. Seest thou not that we have in our own flesh itself many defects? For one man, for instance, is lame, another has his feet distorted, another his hands withered, another some other member weak; and yet nevertheless he does not grieve at it, nor cut it off, but oftentimes prefers it even to the other. Naturally enough; for it is part of himself. As great love as each entertains towards himself, so great he would have us entertain towards a wife. Not because we partake of the same nature; no, this ground of duty towards a wife is far greater than that; it is that there are not two bodies but one; he the head, she the body. And how saith he elsewhere "and the Head of Christ is God"? This I too say, that as we are one body, so also are Christ and the Father One. And thus then is the Father also found to be our Head. He sets down two examples, that of the natural body and that of Christ's body.

When, therefore, the mingled cup and the manufactured bread receives the Word of God, and the Eucharist of the blood and the body of Christ is made, from which things the substance of our flesh is increased and supported, how can they affirm that the flesh is incapable of receiving the gift of God, which is life eternal, which [flesh] is nourished from the body and blood of the Lord, and is a member of Him?-even as the blessed Paul declares in his Epistle to the Ephesians, that "we are members of His body, of His flesh, and of His bones." He does not speak these words of some spiritual and invisible man, for a spirit has not bones nor flesh; but [he refers to] that dispensation [by which the Lord became] an actual man, consisting of flesh, and nerves, and bones,-that [flesh] which is nourished by the cup which is His blood, and receives increase from the bread which is His body. And just as a cutting from the vine planted in the ground fructifies in its season, or as a corn of wheat falling into the earth and becoming decomposed, rises with manifold increase by the Spirit of God, who contains all things, and then, through the wisdom of God, serves for the use of men, and having received the Word of God, becomes the Eucharist, which is the body and blood of Christ; so also our bodies, being nourished by it, and deposited in the earth, and suffering decomposition there, shall rise at their appointed time, the Word of God granting them resurrection to the glory of God, even the Father, who freely gives to this mortal immortality, and to this corruptible incorruption, because the strength of God is made perfect in weakness, in order that we may never become puffed up, as if we had life from ourselves, and exalted against God, our minds becoming ungrateful; but learning by experience that we possess eternal duration from the excelling power of this Being, not from our own nature, we may neither undervalue that glory which surrounds God as He is, nor be ignorant of our own nature, but that we may know what God can effect, and what benefits man receives, and thus never wander from the true comprehension of things as they are, that is, both with regard to God and with regard to man.