Albert Barnes 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)

He that saith, I know him, He who professes to be acquainted with the Saviour, or who professes to be a Christian.

And keepeth not his commandments. What he has appointed to be observed by his people; that is, he who does not obey him.

Is a liar. Makes a false profession; professes to have that which he really has not. Such a profession is a falsehood, because there can be no true religion where one does not obey the law of God.