Unbelief, John wrote, should not be surprising.  God had prophesied ‘blind eyes’ and ‘deadened hearts’ 700 years previously through Isaiah (Isaiah 6:6-13).  Over many centuries God’s people had seen many miracles and heard truth which was crystal clear, but they refused to believe (Luke 11:47-51).  On the other hand, many did believe, including some of the religious leaders; but they were frightened to admit their faith because of what other people would think of them. They were worried about being excluded from the community of the synagogue – particularly those who were seen as important religious officials.
 
So, why did some believe and others not?  Only God can open blind eyes and enliven dead hearts.  God wants everybody to be saved and come to a knowledge of the truth (2 Peter 3:9), but His people had consistently rejected His revelation.  Because they would not believe (John 12:37), therefore they could not believe (John 12:39-40).  Their hard hearts were confirmed.  God knows every heart and will not allow the truth about Jesus to become a plaything.
 
Although many did believe, they were unwilling to confess their faith - putting their salvation at risk (Romans 10:9-11 says, “ … if you declare with your mouth, ‘Jesus is Lord,’ and believe in your heart that God raised him from the dead, you will be saved.  For it is with your heart that you believe and are justified, and it is with your mouth that you profess your faith and are saved.  As Scripture says, ‘Anyone who believes in him will never be put to shame.’")
 
It is very dangerous to refuse to believe in Jesus.  We do not know when God will confirm the hardness of someone’s heart.  It is also dangerous to believe but refuse to confess your faith in Jesus, because of fear of what others will think and do.  The only way to go forward in Christ is to trust in Him and tell somebody else.  That may be more difficult where the church is under persecution.  But confessing our faith is still an essential part of belonging to the Body of Christ, letting others know that we are part of the same Body, and glad to join with others to bring praise to God.