knowing that such a one is perverted, and sinneth, being self-condemned.

Clearly he is in error and a sinner, being self-judged.

εξευρων οτι διεφθαρη ο τοιουτος και αμαρτανει, ων αυτοκατακριτος.

Knowing that he that is such is subverted, and sinneth, being condemned of himself.