Expositor's Bible Commentary Commentary 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, cannot love God whom he hath not seen." — 1 John 4:20 (ASV)

The confidence we have in knowing that God loves us delivers us from fear but not from responsible action. In fact, God’s love for us and in us sets us free to love our brother and sister even as God loves them. To fail this test of love proves that one’s claim to love God is a lie—just as the previous claims to have fellowship with God while walking in darkness (1:6), to know him while disobeying his commands (2:4), or to possess the Father while denying his Son were lies (2:22–23). John has a double sense in “liar.” A liar does not speak the truth in that what he claims is false, and his actions show that he has divorced himself from the reality of God.

The second part of the verse is problematic. It most likely means that if one fails the test of loving a visible brother, such a one makes it certain that he or she does not love the invisible God; this proves that such a person has no true love at all.