4 Now let us examine, and to the best of our ability explain, the meaning of the words of Holy Scripture, which our opponents seize and wrest to their own sense, and urge against us for the destruction of the glory of the Only-begotten. First of all take the words “I live because of the Father,” for this is one of the shafts hurled heavenward by those who impiously use it. These words I do not understand to refer to the eternal life; for whatever lives because of something else cannot be self-existent, just as that which is warmed by another cannot be warmth itself; but He Who is our Christ and God says, “I am the life.” I understand the life lived because of the Father to be this life in the flesh, and in this time.
Of His own will He came to live the life of men. He did not say “I have lived because of the Father,” but “I live because of the Father,” clearly indicating the present time, and the Christ, having the word of God in Himself, is able to call the life which He leads, life, and that this is His meaning we shall learn from what follows. “He that eats me,” He says, “he also shall live because of me;” for we eat His flesh, and drink His blood, being made through His incarnation and His visible life partakers of His Word and of His Wisdom.
For all His mystic sojourn among us He called flesh and blood, and set forth the teaching consisting of practical science, of physics, and of theology, whereby our soul is nourished and is meanwhile trained for the contemplation of actual realities. This is perhaps the intended meaning of what He says.
Source: Letters (New Advent)