What does John 4:49 mean?

It's easy to sympathize with the man's approach to Jesus. As limited people, we often find ourselves only able to focus on one thing at a time. Jesus is making a theological point (John 4:48), but the man is in no condition to debate. His child is nearly dead (John 4:47), so all he can think of is getting Jesus to come back to Capernaum for healing. Jesus' purpose in making these statements is not to dismiss the man's need, but to test his faith.

Biblical "faith" is not simply mental knowledge. It's an act of trust: choosing to rely on those things we do know despite the things we don't know. Apparently, this man already had some level of belief—intellectual knowledge—that Jesus could heal his son. This might have been a last, desperate attempt when all other medicine had failed. He thinks that Jesus can do something, or he would not have come all the way to Cana. The real question is whether the man has faith in Christ.

In other words, wishing that Jesus can heal is different from faith—trust—that He can heal, or will heal. The next verse will show Jesus putting this challenge to the man directly, and his response.