A.T. Robertson Commentary 1 John 2:4

"He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him;" — 1 John 2:4 (ASV)

I know him (Εγνωκα αυτον). Perfect active indicative with recitative οτ like quotation marks just before it. This is one of the pious platitudes, cheap claptrap of the Gnostics, who would bob up in meetings with such explosions. John punctures such bubbles with the sharp addition "and keepeth not" (ο μη τηρων, present active linear participle). "The one who keeps on saying: 'I have come to know him,' and keeps on not keeping his commandments is a liar" (ψευστης, just like Satan, John 8:44 and like 1 John 1:8,10), followed by the negative statement as in 1:8,10. There is a whip-cracker effect in John's words.