If a man say, I love God, and hateth his brother - His Christian brother; or, in a larger sense, any man. The sense is, that no man, whatever may be his professions and pretensions, can have any true love to God, unless he loves his brethren.
He is a liar - Compare the notes at 1 John 1:6. It is not necessary, in order to a proper interpretation of this passage, to suppose that he “intentionally” deceives. The sense is, that this must be a false profession.
For he that loveth not his brother whom he hath seen ... - It is more reasonable to expect that we should love one whom we have seen and known personally, than that we should love one whom we have not seen. The apostle is arguing from human nature as it is, and everyone feels that we are more likely to love one with whom we are familiar than one who is a stranger. If a professed Christian, therefore, does not love one who bears the divine image, whom he sees and knows, how can he love that God whose image he bears, whom he has not seen? Compare the notes at 1 John 3:17.