He that eateth my flesh and drinketh my blood dwelleth in me and I in him. As the living Father sent me, and I live by the Father, so he that eateth me, he too shall live by me (John 6:56-57).

As  if one should join wax with other wax, he will surely see (I suppose) the one in the other.

In like manner he who receives the flesh of our Saviour Christ and drinks His Precious Blood, as He says, is found one with Him.

Such a one is commingled as it were and immingled with Him through the participation, so that he is found in Christ, and Christ again in him.

Thus was Christ teaching us in the Gospel too according to Matthew, saying The kingdom of heaven is like unto leaven, which a woman took and hid in three measures of meal, till the whole was leavened.

[…] As then Paul says that a little leaven leavens the whole lump, so the least portion of the Blessing blends our whole body with itself, and fills it with its own mighty working, and so Christ comes to be in us, and we again in Him.

[…] When the Son says that He was sent, He signifies His incarnation, and nothing else.

And when we speak of His Incarnation, we mean that He was made man complete.

The Father (He says) has made me man, and since I God the Word, was begotten life of that which is by nature life, and, made man, have filled my temple, that is, my body, with my own nature.

In like manner shall he also who eats my flesh live because of me.

I took mortal flesh and dwelt in it, being by nature life, because I am of the living Father.

I re-elemented it wholly into my own life.

I have not been overcome of the corruption of the flesh but have rather overcome it, as God.

Although I was made (He says) flesh (for this is what being sent means), I live again because of the living Father, retaining in myself the natural excellence of Him that begot me.

In the same way he who, by the participation of my flesh, receives me in himself shall live, wholly trans-elemented entire into me, who am able to give life.

For I am (as it were) of life-giving root, that is God the Father.

Cyril of Alexandria (c. 376-444): Commentary on John, book 4.