1 John 2:3

3AndΚαὶbyἐνthisτούτῳwe knowγινώσκομενthatὅτιwe have come to knowἐγνώκαμενHimαὐτόν,ifἐὰνtheτὰςcommandmentsἐντολὰςof Himαὐτοῦwe should keepτηρῶμεν.

And by this we know that we have known Him, if we may keep His commandments.