Jesus had done many miraculous signs before the people, but they didn't believe in him.
References for John 12:37
This was to fulfill the word of the prophet Isaiah: Lord, who has believed through our message? To whom is the arm of the Lord fully revealed?
References for John 12:38
Isaiah explains why they couldn't believe:
He made their eyes blind and closed their minds so that they might not see with their eyes, understand with their minds, and turn their lives around— and I would heal them.
References for John 12:40
Isaiah said these things because he saw Jesus' glory; he spoke about Jesus.
Even so, many leaders believed in him, but they wouldn't acknowledge their faith because they feared that the Pharisees would expel them from the synagogue.
They believed, but they loved human praise more than God's glory.
Jesus shouted, "Whoever believes in me doesn't believe in me but in the one who sent me.
References for John 12:44
Whoever sees me sees the one who sent me.
I have come as a light into the world so that everyone who believes in me won't live in darkness.
If people hear my words and don't keep them, I don't judge them. I didn't come to judge the world but to save it.
Whoever rejects me and doesn't receive my words will be judged at the last day by the word I have spoken.
I don't speak on my own, but the Father who sent me commanded me regarding what I should speak and say.
I know that his commandment is eternal life. Therefore, whatever I say is just as the Father has said to me."