1 John 2:4

² And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world.

³ And hereby we do know that we know him, if we keep his commandments.

He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him.

⁵ But whoso keepeth his word, in him verily is the love of God perfected: hereby know we that we are in him.

⁶ He that saith he abideth in him ought himself also so to walk, even as he walked.

Do read the surrounding verses too, because the context often says more than a single verse.

Compare

BSB: If anyone says, “I know Him,” but does not keep His commandments, he is a liar, and the truth is not in him.
KJV: He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him.
WEB: One who says, “I know him,” and doesn’t keep his commandments, is a liar, and the truth isn’t in him.
ASV: He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him;
DARBY: He that says, I know him, and does not keep his commandments, is a liar, and the truth is not in him;
BLB: The one saying, “I have known Him,” and not keeping His commandments, he is a liar, and the truth is not in him.

ÅB: Den som sier: Jeg kjenner ham, og ikke holder hans bud, han er en løgner, og i ham er ikke sannheten;
OTB: Den som sier: "Jeg har kommet til å kjenne Ham," men ikke holder Hans bud, bedrar seg selv, og sannheten er ikke i ham;
B1930: Den som sier: Jeg kjenner ham, og ikke holder hans bud, han er en løgner, og i ham er ikke sannheten;

1 John 1:6
If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth:
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Titus 1:16
They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate.
Read in context
James 2:14–16
What doth it profit, my brethren, though a man say he hath faith, and have not works? can faith save him?
Read in context
1 John 1:8
If we say that we have no sin, we deceive ourselves, and the truth is not in us.
Read in context
1 John 4:20
If a man say, I love God, and hateth his brother, he is a liar: for he that loveth not his brother whom he hath seen, how can he love God whom he hath not seen?
Read in context
1 John 2:9
He that saith he is in the light, and hateth his brother, is in darkness even until now.
Read in context
Hosea 8:2–3
Israel shall cry unto me, My God, we know thee.
Read in context
1 John 1:10
If we say that we have not sinned, we make him a liar, and his word is not in us.
Read in context