From: John 8:51-59
Jesus Warns the Unbelieving Jews (Continuation)
(Jesus said to the Jews,)  "Truly, truly, I say to you, if any one keeps My word, he will never see death."  The Jews said to Him, "Now we know that You have a demon. Abraham died, as did the prophets; and You say, `If anyone keeps My word, he will never taste death.'  Are you greater than our father Abraham, who died? And the prophets died! Who do You claim to be?"  Jesus answered, "If I glorify Myself, My glory is nothing; it is My Father who glorifies Me, of whom you say that He is your God.  But you have not known Him; I know Him. If I said I do not know Him, I should be a liar like you; but I do know Him and I keep His word.  Your father Abraham rejoiced that he was to see My day; he saw it and was glad."  The Jews then said to Him, "You are not yet fifty years old, and have You seen Abraham?"  Jesus said to them, "Truly, truly, I say to you, before Abraham was, I am."  So they took up stones to throw at Him; but Jesus hid Himself, and went out of the temple.
51-53. "He will never see death": our Lord promises eternal life to those who accept His teaching and remain faithful to it.
Sin, as the Fourth Gospel teaches, is death of the soul; and sanctifying grace, life (cf. John 1:4, 13; 3:15, 16. 36; etc.). Through grace we enter eternal life, a pledge of the Glory we shall attain beyond this earthly life and which is the true Life. Blinded by their hostility, the Jews do not want to listen to the Lord and therefore they fail to understand Him.
55. The knowledge our Lord is speaking about implies more than intellectual knowledge. The Old Testament speaks of this "knowing" in the sense of love, faithfulness, generous self-surrender. Love for God is a consequence of the certain knowledge we have of Him, and at the same time the more we love God, the better we get to know Him.
Jesus, whose holy human nature was intimately united (though not mixed) with His divinity in the one Person of the Word, continues to assert His singular and ineffable knowledge of the Father. But this accurate language of Jesus is absolutely incomprehensible to those who close themselves to faith: they even think He is blaspheming (cf. verse 59).
56. Jesus presents Himself as the fulfillment of the hopes of the Old Testament patriarchs. They had stayed faithful, eager to see the Day of Salvation. Referring to their faith, St. Paul exclaims: "These all died in faith, not having received what was promised, but having seen it and greeted it from afar, and having acknowledged that they were strangers and exiles on the earth" (Hebrews 11:13). The most outstanding of those patriarchs was Abraham, our father in faith (cf. Galatians 3:7), who received the promise of being father of an immense people, the chosen people from whom would be born the Messiah.
The future fulfillment of the messianic promises was a source of great joy for Abraham: "Abraham, our father, who was set apart for the future accomplishment of the Promise, and who hoped against hope, receives when his son Isaac is born the prophetic firstfruits of this joy. This joy becomes transfigured through a trial touching death, when this only son is restored to him alive, a prefiguring of the resurrection of the One who was to come: the Son of God, promised for the redeeming sacrifice. Abraham rejoiced at the thought of seeing the Day of Christ, the Day of Salvation: he "saw it and was glad" (Paul VI, "Gaudete In Domino", II).
Jesus moves on a plane superior to that of the patriarchs, for they only saw prophetically, from "afar", the day of Christ, that is, the actual event of the Redemption, whereas it is Christ who brings it to pass.
58. Jesus' reply to the skeptical remarks of the Jews contains a revelation of His divinity. By saying "Before Abraham was, I am" our Lord is referring to His being eternal, because He is God. Therefore, St. Augustine explains: "Acknowledge the Creator, discern the creature. He who was speaking was a descendant of Abraham, but that Abraham might be made, before Abraham He was" (St. Augustine, "In Ioann. Evang.", 43, 17).
The Fathers recall, in connection with the words of Christ, the solemn theophany of Sinai: "I AM WHO I AM" (Ex 3:14), and also St. John's distinction in the prologue to his Gospel, between the world which "was made" and the Word which "was" from all eternity (cf. John 1:1-3). The words, "I am", used by Jesus so absolutely are the equivalent therefore, of His affirming His eternity and His divinity. Cf. note on John 8:21-24.
[The note on John 8:21-24 states:
21-24. At the outset of His public ministry, Jesus could be seen to have all the features of the promised Messiah; some people recognized Him as such and became His followers (cf. John 1:12-13; 4:42; 6:69; 7:41); but the Jewish authorities, although they were expecting the Messiah (cf. John 1:19ff), persisted in their rejection of Jesus. Hence the warning to them: He is going where they cannot follow, that is, He is going to Heaven, which is where He has come from (cf. John 6:41ff), and they will keep looking out for the Messiah foretold by the prophets; but they will not find Him because they look for Him outside of Jesus, nor can they follow Him, for they do not believe in Him. You are of the world, our Lord is saying to them, not because you are on earth but because you are living under the influence of the prince of this world (cf. John 12:31; 14:30; 16:11); you are his vassals and you do his deeds (cf. 8:44); therefore, you will die in your sin. "We are all born with sin", St. Augustine comments, "all by our living have added to what we were by nature, and have become more of this world than we then were, when we were born of our parents. Where would we be if He had not come, who had no sin at all, to loose all sin? The Jews, because they did not believe in Him, deserved to have it said to them, You will die in your sin" ("In Ioann. Evang.", 38, 6).
The salvation which Christ brings will be applied to those who believe in His divinity. Jesus declares His divinity when He says "I am He", for this _expression, which He repeats on other occasions (cf. John. 8:28; 13:19), is reserved to Yahweh in the Old Testament (cf. Deuteronomy 32:39; Isaiah 43:10-11), where God, in revealing His name and therefore His essence, says to Moses "I AM WHO I AM" (Exodus 3:14). In this profound way God says that He is the Supreme Being in a full, absolute sense, that He is dependent on no other being, that all other things depend on Him for their being and existence. Thus, when Jesus says of Himself, "I am He", He is revealing that He is God.]
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.