What does John 4:51 mean?

This man is described in verse 46 using the Greek term basilikos, which implies royal connections. He is either a court official, a nobleman, or some other high-ranking person. Given that his son is in dire straits (John 4:47), going to Jesus for healing was probably his last-ditch effort to save the boy. Jesus' actions in Jerusalem (John 2:23) and Sychar (John 4:40–41) have made enough impact that others are hearing about Him. Coming to Jesus is an act which proves the man has some knowledge, and some hope. Jesus, however, makes the point that many people will not believe unless they see miracles. This is not the same as "faith," which requires trust. Jesus' instructions to the man in verse 50 are meant to test that very trait. Knowing that Jesus is a healer is not "trust." Hoping that He will heal is not "trust." Insisting on Jesus coming back with him certainly implies that he felt a need to control the situation. However, being willing to walk away, with only His word as a promise, requires genuine, biblical trust, which is what the Scriptures mean by "faith."

The timing of this encounter shows that the man's request was already granted, before he even knew it. This is a common aspect of our relationship to God, which is often overlooked. There are times when we cannot see the answers to our prayers, but that does not mean God has not answered them. In this case, the man traveled quite some way before getting the news—the servants refer to the moment of healing as "yesterday" (John 4:52). During that time, though he did not know it, God had already granted his request.