He that saith I know him
God or Christ, as the Gnostics did, who pretended to great, even perfect, knowledge of divine things:
and keepeth not his commandments;
which the above persons had no regard to, and as many who profess great light and knowledge in our days show no concern for:
is a liar;
he contradicts what he says, and gives the lie to it; for though in words he professes to know God, in works he denies him, and which betrays his ignorance of him:
and the truth is not in him;
there is no true knowledge of God and Christ in him; nor is the truth of the Gospel in his heart, however it may be in his head; nor is the truth of grace in him, for each of these lead persons to obedience. The Ethiopic version renders it, "the truth of God is not with him"; (See Gill on 1 John 1:8).