One who says, "I know him," and doesn't keep his commandments, is a liar, and the truth isn't in him.
"The three assertions about knowing God, abiding in him, and being in the light (as he himself is in the light, 1 John 2:7), are parallel versions of a single claim to be in a right relationship with the Father through the Son." [Note: Smalley, p. 59.] 