Praised be Jesus and Mary, now and forever. 
In today’s Gospel, Christ continues to dispute with the Jews, and he succeeds in bringing many to believe in him, albeit with an imperfect faith. Others, however, persist in refusing to believe in his divinity, and those who persist in this refusal until death will die in their sins. This is why Christ said, “Where I am going, you cannot come.” They cannot come with him to heaven because they will die in their sins for their lack of belief.
St. Augustine understands Jesus to say this out of foreknowledge, that is, he knows that they will never repent and so will die in their sins. Later, however, Christ makes it conditional when he says, “If you do not believe that I am, you will die in your sins.” Thus they could still believe and be saved, and St. Augustine acknowledges that some of them did in fact eventually believe. So while Christ had foreknowledge of who would never be saved, this did not include everyone to whom he was speaking. He spoke at first as if it did in order to scare them into repentance, just as Jonah said that Nineveh would be destroyed without mentioning the possibility of salvation by repentance.
This is the condition: if you do not believe that I am, you will die in your sins. Belief in Christ’s divinity is necessary for salvation, at least for those to whom it has been revealed, for this is what he means by “I am”: “I am who am,” Yahweh, the God of Abraham, Isaac, and Jacob. They don’t understand this, or they pretend not to understand, taking “I am” as predication, whereas he means existence. Because Christ is divine, he is inseparable from the Father. Even as regards his human nature, the Father never leaves him because he always does what is pleasing to him. Only sin separates us from God.
The rejection of Christ by the Jews will lead them to have him crucified, but with consequences full of mystery. This mystery was foreshadowed in the book of Numbers, and the book of Wisdom interpreted it before the coming of Christ. In the desert, the chosen people accused God of leading them out into the desert to die. The book of Wisdom explains God’s reaction, to remind them of your oracles. They were bitten, and then they were quickly delivered, lest they should fall into deep forgetfulness and become unresponsive to your kindness.
God did not want them to die in their sins, and mere words had proved insufficient time and time again, so he turned to harsher measures. He killed some to save the rest, whom he promptly saved when they asked for help. The healing came about by a curious means: a bronze serpent lifted up on a pole. The book of Wisdom explains that whoever turned toward it was saved, not by what he saw, but by you, the Savior of all. Neither herb nor poultice cured them, but it was your word, O Lord, which heals all men.
And yet, how were they healed by the word if they were healed by looking at it and not by hearing something? The Greek that “word” translates is “Logos,” and Christ is the Logos of the Father, the Word of God. So we see that it was Christ who healed them. He did this because the bronze serpent represented his future victory on the cross, by which we are saved from the ancient serpent. The devil is said to have been the greatest of angels before his fall, which would put him in the choir of the seraphim, so he is fittingly represented by a seraph serpent.
This is the serpent who spiritually bites us when we doubt God’s goodness and rebel against him by sin. His poison is lies. Those who receive this poison into themselves and act on it are deprived of eternal life. The Fathers give various reasons why it was appropriate for Christ to be prefigured by a bronze serpent. Saint Bede says that the statue looked like a serpent but had no poison in it. Similarly, Christ came in the likeness of sinful flesh, but there was no sin in him.
Saint Ephraim wrote, “It was revealed through this brazen serpent, which by nature cannot suffer, that he who was to suffer on the cross was one who by nature cannot die.” So as bronze serpents do not die by nature, so Christ by nature could not die, and yet took a human nature so that he would be able to die. In today’s Gospel, Christ indirectly referred to the bronze serpent when he said, “When you lift up the Son of Man, then you will realize that I am.” This is the second time he spoke of being lifted up, and so it calls to mind the first time when he said, “As Moses lifted up the serpent in the wilderness, so must the Son of Man be lifted up, that whoever believes in him may have eternal life.”
Lack of faith in God is the cause of eternal death for the soul. Faith in Christ is the foundation of eternal life. God does not want men to die in the sin of unbelief, and therefore he orders that his Son be lifted up on the cross so that those who look on him may believe and have eternal life. The cross bears witness to a love so great it can only be divine. So when Christ says, “When you lift up the Son of Man, then you will realize that I am,” he is telling those Jews that some of them at least will recognize his divinity as a result of his crucifixion.
Their leaders did not know this when they had him killed, for if they had known, Saint Paul says, they would not have crucified the Lord of glory. And Jesus said on the cross, “Father, forgive them, for they know not what they do.” But many of the Jews, when they saw in the cross, death, and resurrection of Jesus Christ such patience, charity, zeal, and such great prodigies and miracles, such as the earthquakes, the eclipse, the people rising from the dead, by these things they were moved to compunction to believe in him.
This was especially so starting at Pentecost, when the apostles’ preaching brought many to repentance. Moreover, it was the crucifixion that merited the outpouring of the Holy Spirit, with which the apostles preached. It also merited the grace of conversion for the Jews who believed. About 3,000 Jews were baptized on the day of Pentecost, and not long after that, the number rose to 5,000. Christ obtained all this by his cross, and obtained it from his Father.
Let us, too, look on the one we have pierced by our sins, meditating his Passion in these last two weeks of Lent. Let us ask Our Lady, “May we feel what you have felt,” as in the Stabat Mater, “teach me how to meditate the Passion.” 
Praised be Jesus and Mary, now and forever.