9 And how has He? Even as the Father has. Hear Himself saying, “For as the Father has life in Himself, so also has He given to the Son to have life in Himself.” Brethren, I shall speak as I shall be able. For these are those words that perplex the puny understanding. Why has He added, “in Himself”? It would suffice to say, “For as the Father has life, so also has He given to the Son to have life.” He added, “in Himself:” for the Father “has life in Himself,” and the Son has life in Himself.
He meant us to understand something in that which He says, “in Himself.” And here a secret matter is shut up in this word; let there be knocking, that there may be an opening. O Lord, what is this that You have said? Wherefore have You added, “in Himself”? For did not Paul the apostle, whom You made to live, have life? He had, said He. As for men that were dead to be made alive, and at Your word to pass unto life by believing; when they shall have passed, will they not have life in You?
They shall have life; for I said also a little before, “Whoso hears my words, and believes Him that sent me, has eternal life.” Therefore those that believe in You have life; and You have not said, “in themselves.” But when You speak of the Father, “even as the Father has life in Himself;” again, when You speak of Yourself, Thou said, “So also has He given to the Son to have life in Himself.” Even as He has, so gave He to have. Where has He? “In Himself.” Where gave He to have?
“In Himself.” Where has Paul life? Not in himself, but in Christ. Where have you, believer? Not in yourself, but in Christ. Let us see whether the apostle says this: “Now I live; but not I, but Christ lives in me.” Our life, as ours, that is, of our own personal will, will be only evil, sinful, unrighteous; but the life in us that is good is from God, not from ourselves; it is given to us by God, not by ourselves. But Christ has life in Himself, as the Father has, because He is the Word of God.
With Him, it is not the case that He lives now ill, now well; but as for man, he lives now ill, now well. He who was living ill, was in his own life; he who is living well, is passed to the life of Christ. You are made a partaker of life; you were not that which you have received, but wast one who received: but it is not so with the Son of God as if at first He was without life, and then received life. For if thus He received life, He would not have it in Himself. For, indeed, what is in Himself? That He should Himself be the very life.
Source: Tractates on the Gospel of John (New Advent)