1 John 4:3

He writes these things so that they will not sin, but if anyone does sin, they have an advocate with the Father, Jesus Christ the righteous, who is the propitiation for the sins of the whole world. The assurance of knowing God comes from keeping His commandments. Whoever claims to know Him but does not keep His commandments is a liar. The author emphasizes the commandment to love one another, which is both an old commandment they have had from the beginning and a new one, because the darkness is passing away and the true light is now shining. Anyone who claims to be in the light but hates his brother is still in darkness. The author warns against loving the world or the things in the world, because all that is in the world—the lust of the flesh, the lust of the eyes, and the pride of life—is not from the Father but from the world, which is passing away. He also warns that it is the last hour and that many antichrists have come, who deny that Jesus is the Christ. 3–4: Love and discernment The author marvels at the love the Father has bestowed upon them, that they should be called the children of God. As children of God, they are called to purify themselves, just as He is pure. He who sins is of the devil, but the Son of God was manifested to destroy the works of the devil. Those born of God do not continue in sin. The distinction between the children of God and the children of the devil is clear: those who do not practice righteousness or love their brother are not of God. The message from the beginning is to love one another, unlike Cain who murdered his brother. Love for the brethren is a sign of having passed from death to life. This love is not just in word or tongue, but in deed and in truth.