He confirms the judgment of the Apostle by the authority of the Lord.
And though this is the saying of an Apostle, yet it is the very doctrine of the Lord. For the same Person says this to Christians by His Apostle, who had Himself said something very like it to Jews in the gospel, when He said: “But now ye seek to kill me, a man, who have spoken the truth to you, which I heard of God: for I am not come of Myself, but He sent me.” 2517 He clearly shows that He is both God and man: man, in that He says that He is a man: God, in that He affirms that He was sent. For He must have been with Him from whom He came: and He came from Him, from whom He said that He was sent. Whence it comes that when the Jews said to Him, “Thou art not yet fifty years old and hast Thou seen Abraham?” He replied in words that exactly suit His eternity and glory, saying, “Verily, verily, I say unto you, Before Abraham came into being, I am.” 2518 I ask then, whose saying do you think this is? Certainly it is Christs without any doubt. And how could He who had been but recently born, say that He was before Abraham? Simply owing to the Word of God, with which He was entirely united, so that all might understand the closeness of the union of Christ and God: since whatever God said in Christ, that in its fulness the unity of the Divinity claimed for Himself. But conscious of His own eternity, He rightly then when in the body, replied to the Jews, with the very words which He had formerly spoken to Moses in the Spirit. For here He says, “Before Abraham came into being, I am.” But to Moses He says, “I am that I am.” 2519 He certainly announced the eternity of His Divine nature with marvellous grandeur of language, for nothing can be spoken so worthily of God, as that He should be said ever to be. For “to be” admits of no beginning in the past or end in the future. And so this is very clearly spoken of the nature of the eternal God, as it exactly describes His eternity. And this the Lord Jesus Christ Himself, when He was speaking of Abraham, showed by the difference of terms used, saying, “Before Abraham came into being I am.” Of Abraham he said, “Before he came into being:” Of Himself, “I am,” for it belongs to things temporal to come into being: to be belongs to eternity. And so “to come into being” He assigns to human transitoriness: but “to be” to His own nature. And all this was found in Christ who, by virtue of the mystery of the manhood and Divinity joined together in Him who ever “was,” could say that He already “was.”
S. John 8:40, 42.586:2518
Exod. iii. 14.