When he heard that Jesus had come out of Judea into Galilee, he went to Him and implored Him to come down and heal his son, for he was at the point of death. So the man believed the word that Jesus spoke to him, and he went his way. Then he inquired of them the hour when he got better. And he himself believed, and his whole household. This again is the second sign Jesus did when He had come out of Judea into Galilee.
People say they'll believe something when they see it.
The Gospel today tells us that John the Baptist was put in prison. He needed to go pick up where John left off. The nobleman didn't believe his son was healed until his servants reported that the son was okay. And even then, the nobleman compared the time of his recovery with the time he was talking to Jesus. We are so sure miracles can't happen that we even doubt the existance of God, Himself.