One who was there had been an invalid for thirty-eight years. When Jesus saw him lying there and knew that he had been in this condition for a long time, he asked him, “Do you want to get well?” “Sir,” the invalid replied, “I have no one to help me into the pool when the water is stirred. While I am trying to get in, someone else goes down ahead of me.” Then Jesus said to him, “Get up! Pick up your mat and walk.” At once the man was cured; he picked up his mat and walked.
We are back to the theme of water again with the same implication; the ritual of water is insufficient: the power of Christ is sufficient. We do not know what caused this man's invalidity, but we must assume it is some form of paralysis that had lasted a very long time. Indeed, Jesus questions his faith, "Don't you even want to get well?" From the rest of teh story we do not get the impression that this man was a very nice sort. But there we are; it isn't just nice people that are saved.
There is no written record elsewhere of this first come-first served dispensation of healing and it may have been mere superstition. Just as the Christian faith can lapse into superstition, so could Judaism. Jesus' healing does not use the pool or water at all, merely the word of command. and like the man let down through the roof, he picked up his bed and walked.
The healing was complete and instantaneous. The muscles regrew to make him strong enough to carry the mat and any contractions stretched to make him able to walk.