That question may seem to have things backwards, but it actually arises from a passage in John’s Gospel:
“When Jesus was in Jerusalem during the Passover festival, many believed in his name because they saw the signs that he was doing. But Jesus on his part would not entrust himself to them, because he knew all people and needed no one to testify about anyone; for he himself knew what was in everyone.” (John 2:23-24)
The Greek word that is translated “believed” is pisteuo, the usual New Testament word for faith. But the same Greek word is used later in the passage, where it is translated into English as “entrust.” The Gospel writer intentionally used the same word in both directions, their response to him and his response to them. No English translation that I’ve discovered has been able to capture this by using the same word both times. Though it may sound a little strange, my suggestion of a fair translation would be “They believed in Jesus, but he didn’t believe in them.”
The Greek word pisteuo in the New Testament is often followed by the preposition eis, which means “into,” rather than en, which means “in.” So belief is seen as active, not passive. It’s not just a matter of mental agreement. There is movement, change, commitment. They “believed into” Jesus, which means they became his followers. But he didn’t “believe into” them because he knew what was deeper in their hearts.
The Old Testament equivalent of pisteuo is amen. We use this word at the end of our prayers: “Amen!” This Hebrew word has a root meaning of solid, unshakable support or confidence. When a person says “Amen!” it implies whole-person commitment, meaning essentially, “I’ll stake my life on it.”
Four thousand years ago, it was said of Abraham, the pioneer of our faith, “He believed the Lord, and the Lord reckoned it to him as righteousness.” (Genesis 15:6) The Hebrew word translated “believed” is amen. The genuineness and depth of his faith was proven by the fact that he left the security of his homeland to follow God into an unknown and dangerous future. Abraham’s faith was Amen!-faith, and that’s why the Lord “reckoned it to him as righteousness.” Abraham Amen-ed God, so God Amen-ed Abraham.
By contrast the “believers” encountered by Jesus, described in John 2, did not have a faith that reached the Amen!-level. The surrounding context in John’s Gospel helps us to see this. The preceding verses tell about Jesus’ first dramatic public miracle, the changing of water into wine at a wedding feast (2:1-11). This is what attracted the attention of the crowds and led many to believe in him. However, our passage is followed by the story of how Nicodemus came privately to learn more from Jesus and heard Jesus tell him about his need to be “born again” (3:1-8). The water-to-wine miracle seemed to make them believe in him, but unless they experienced the more important miracle, being ‘born again,” he would not believe in them.
You believe in Jesus. You are proud to call yourself a Christian. You can be found in church every Sunday with people who share your faith. You believe in Jesus, but does Jesus believe in you? Do you hear his “Amen!” in your heart?