A.T. Robertson Commentary John 5:14

"Afterward Jesus findeth him in the temple, and said unto him, Behold, thou art made whole: sin no more, lest a worse thing befall thee." — John 5:14 (ASV)

Findeth him (ευρισκε αυτον). Dramatic present as in 1:45, possibly after search as in 9:35.

Sin no more (μηκετ αμαρτανε). "No longer go on sinning." Present active imperative with μηκετ, a clear implication that disease was due to personal sin as is so often the case. Jesus used the same words to the woman taken in adultery in the spurious passage (John 8:11). He had suffered for 38 years. All sickness is not due to personal sin (9:3), but much is and nature is a hard paymaster. Jesus is here living up to his name (Matthew 1:21).

Lest a worse thing befall thee (ινα μη χειρον σο τ γενητα). Negative final clause with second aorist middle subjunctive of γινομα. Χειρον is comparative of κακος, bad. Worse than the illness of 38 years, bad as that is. He will now be sinning against knowledge.