The greater difficulty here is implied, through our present dependence upon sense, of loving the invisible God, than men that we daily see and converse familiarly with. Hence, considering the comprehensiveness of these two things, the love of God, and of our brother, that they are the roots of all that duty we owe to God and man, the fulfilling of the whole law, Matthew 22:37-39, he lets us see the falsehood and absurdity of their pretence to eminent piety and sanctity, who neglect the duties of the second table.
Related Commentaries of 1 John 4:20
1 John 4:20
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, how can he love God whom he hath not seen?