Then they said to [Jesus], "Who are You?"
And Jesus said to them, "Just what I have been saying to you from the beginning. I have many things to say and to judge concerning you, but He who sent Me is true; and I speak to the world those things which I heard from Him."
They did not understand that He spoke to them of the Father.
Then Jesus said to them, "When you lift up the Son of Man, then you will know that I am He, and that I do nothing of Myself; but as My Father taught Me, I speak these things. And He who sent Me is with Me. The Father has not left Me alone, for I always do those things that please Him." As He spoke these words, many believed in Him.
In this chapter, Jesus is teaching at the treasury in the temple in Jerusalem. The Jews ask him, "Who are you?" In response, Jesus says that he's been teaching them that all along and that he's been speaking the words of God. To clarify their confusion, Jesus points them to his coming crucifixion and says that when they crucify him, then they will know that He is who he claimed to be. Even as Jesus spoke, many people believed in him.
My mind leapt when I read the words: "when you lift up the Son of Man." Jesus used these words earlier when he spoke to a Jewish religious leader named Nicodemus. On that occasion, Jesus had said, "and as Moses lifted up the serpent in the wilderness, even so must the Son of Man be lifted up, that whoever believes in Him should not perish but have eternal life."
So it led me to wonder ... was Nicodemus present at the temple on this occasion to hear Jesus' teaching? He certainly was in Jerusalem around this time. In the previous chapter (possibly the day before), we see Nicodemus debating with the other religious leaders about what to make of Jesus (John 7:50). We also see him appear later in Jerusalem (John 19:39). It's entirely possible that Nicodemus was present to hear Jesus speak the words here "when you lift up the Son of Man."
If Nicodemus was present...
...might Nicodemus have remembered his conversation with Jesus by night (John 3:1-21). Jesus had declared that "unless one is born again, he cannot see the kingdom of God" and that this is made possible only by faith in the Son of God, who would be given for the salvation of the world.
...might Nicodemus have asked himself the question, "who has Jesus been declaring himself to be from the beginning?" During their evening conversation, Jesus had spoken of himself as the Son of Man who came from heaven (John 3:13). Jesus had also spoken of himself as the Son of Man who would be crucified in order to give eternal life to those who believe (John 3:14-5). Jesus had also spoken of himself as the Son of God, given to the world in love so that eternal life would be made available to those who believe (John 3:16-17).
...might Nicodemus have been one of those many who believed in him? The Pharisees were divided in their opinions of Jesus (John 9:16). Some believed him to be a demon-possessed sinner "because He does not keep the Sabbath" (John 8:48, 8:52, 9:16). And "not only was [He] breaking the Sabbath, but also was calling God His own Father, making Himself equal with God" (John 5:18). In addition, they believed that "no prophet has arisen out of Galilee" (John 7:52).
But Nicodemus was not so certain. He told his fellow Jews, "Does our law judge a man before it hears him and knows what he is doing?" Unlike some of the Jews who believed that Jesus was "not from God, because He does not keep the Sabbath. Others said, 'How can a man who is a sinner do such signs?'" (John 9:16). When Nicodemus came to Jesus by night, he said to Jesus, "Rabbi, we know that You are a teacher come from God; for no one can do these signs that You do unless God is with him." (John 3:2) The man born blind (who was healed shortly after Jesus' teaching at the treasury) agreed: "If this Man were not from God, He could do nothing." (John 9:30)
We might rightly ask, did Nicodemus even come to believe in Jesus? It seems that he did, if he were willing to defile himself by contacting the dead body of Jesus in order to help bury Jesus during the Passover festival (John 19:39). And if Nicodemus came to believe, might he have believed on this day?
We don't know. We won't know. But maybe one day, if he indeed believed, I can ask Nicodemus about the marvelous rebirth that God worked in his heart, calling him out of darkness into His marvelous light (1 Peter 2:9)