If anyone says, “I love God,” and hates his brother, he is a liar; for he who does not love his brother whom he has seen cannot love God whom he has not seen.
But this love cannot exist, except it generates brotherly love. Hence he says, that they are liars who boast that they love God, when they hate their brethren. But the reason he subjoins seems not sufficiently valid, for it is a comparison between the less and the greater: If, he says, we love not our brethren whom we see, much less can we love God who is invisible.
Love to God gives us boldness in the day of judgment. When we love Him truly, we know ourselves loved by Him in return; we can lift our heads before the Judge knowing He is our friend. This assurance comes only from lovers of God.
AI summary
Commenting on 1 John 4:17-21
And this commandment have we from him,.... Either "from God", as the Alexandrian copy and the Vulgate Latin version read; and that to love the brethren is a commandment of God, is clear from Jo1 3:23; or from Christ, for it is also a command of his, even his new commandment, which he has given, and his people have received from him: that he who...