John 5:14

Afterward Jesus findeth him in the temple, and saith unto him, Behold, thou art made whole; sin no more, lest a worse thing befall thee.

This explains the reason for Jesus' disappearance. He wanted a private interview with that man, sparing him the humiliation of having his sinful life exposed before all, a thing that would have been far less effective in the former cripple's case than what happened privately in the temple. Perhaps the man had gone there to praise God for his healing, but this is not stated.

Sin no more ... This shows that sin was connected with the infirmity which had so long debilitated the cripple. There is indeed a connection between sin and suffering. In fact all human sorrows and sufferings, even death itself, head up at last in the fountainhead of the sin of Adam. This is far from teaching that all sickness or suffering is specifically related to the sin of the sufferer. Jesus himself stressed (John 9:3) that the blindness of the man he healed was not related to either his or his parents' sins. Nevertheless, an incredible amount of the world's woe is merely the sins af men returned at last upon their own heads. Trench expressed it thus:

As some eagle pierced with a shaft leathered from its own wing, so many a sufferer, even in this present time, sees and is compelled to acknowledge that his own sin fledged the arrow, which has pierced him and brought him down.[8]

Lest a worse thing befall thee ... What could be worse than being an invalid for thirty-eight years? The fate of unbelievers is worse. Also, there is a temporal application as well; because there is no condition of human wretchedness so bad that further sin might not aggravate and increase it.