"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).

The particular design of these verses is to take forth the precious from the vile. In them the apostle describes one of the vital differences which there is between the sheep and the goats. Of the latter it is said, “They profess that they know God; but in works they deny him” (Ti 1:16). They adopt the same language as the saints, believe the same doctrines, claim to be resting on the finished work of Christ, and are quite sure of their salvation; yet evince little or no concern for His precepts. They talk glibly, but walk carelessly. This is exceedingly solemn, for those who tread not in the way of God’s precepts are strangers to Him.

A man spiritually knows no more than he practices, for spiritual knowledge is radical and influential. It exerts both a restraining and a constraining power, causing its subject to loathe and shun evil and to love and pursue that which is good.

Therefore, they who keep not God’s commandments have no experiential acquaintance with Him. “We cannot know Him as Lord and Father, without being dutiful children and obedient servants” (Calvin)........The defects and deficiencies of the Christian’s life are indeed many, nevertheless the one who has been born again evidences it by habitually walking with God."

~ Arthur Pink, “Exposition of John's First Epistle"