Passage
And this commandment have we from him, that he who loveth God love his brother also.
And this commandment have we from him, that he who loveth God love his brother also.
1 John 4:19 We love, because he first loved us.
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 4:21 And this commandment have we from him, that he who loveth God love his brother also.
The verse centers on "commandment", "loveth", and "brother". It is saying that the verse draws attention to "commandment" and "loveth", so its meaning should be read from those terms before moving to application.
The prior verse says "If a man say I love God...", giving immediate footing for "commandment" and "loveth". In 1 John context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "commandment" and "loveth" with trust shaped by these words, not by a vague optimism outside the passage.