And this commandment have we from him - That is, the command to love a brother is as obligatory as that to love God. If one is obeyed, the other ought to be also; if a man feels that one is binding on him, he should feel that the other is also; and he can never have evidence that he is a true Christian, unless he manifests love to his brethren as well as love to God. See the notes at James 2:10.

That he who loveth God love his brother also - See the notes at John 13:34-35. Compare John 15:12, John 15:17.

This commandment have we - We should love one another, and love our neighbor as ourselves. The love of God and the love of man can never be separated; he who loves God will love his brother; he who loves his brother gives this proof that he loves God, because he loves with a measure of that love which, in its infinitude, dwells in God.

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 1 John 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 loveth God, love his brother also; see John 13:34; which is an argument persuading to attend to the one as well as to the other; for the same command that requires the one, requires the other: and he that transgresses it in one case, is a transgressor of it, as well as in the other.

That (ἵνα)

Not defining the contents of the commandment, but expressing intent. Compare John 13:34, and see on John 15:13.

His brother

"To the persecutor Saul, Christ said, 'Saul, Saul, why persecutest thou Me? I have ascended into heaven, yet still I lie upon earth. Here I sit at the right hand of the Father; there I still hunger, thirst, and am a stranger'" (Augustine).

{17} And this commandment have we from him, That he who loveth God love his brother also.

(17) A second reason, why God cannot be hated and our neighbour loved, because this same lawmaker commanded us both to love him and our neighbour.

4:21 This commandment have we from him. It is God's will that he who loves the Father should love the children also.

4:21 And this commandment have we from him - Both God and Christ. That he who loveth God love his brother - Every one, whatever his opinions or mode of worship be, purely because he is the child, and bears the image, of God. Bigotry is properly the want of this pure and universal love. A bigot only loves those who embrace his opinions, and receive his way of worship; and he loves them for that, and not for Christ's sake.

21. Besides the argument (1Jo 4:20) from the common feeling of men, he here adds a stronger one from God's express commandment (Mt 22:39). He who loves, will do what the object of his love wishes.

he who loveth God-he who wishes to be regarded by God as loving Him.

4:14-21 The Father sent the Son, he willed his coming into this world. The apostle attests this. And whosoever shall confess that Jesus is the Son of God, God dwelleth in him, and he in God. This confession includes faith in the heart as the foundation; makes acknowledgment with the mouth to the glory of God and Christ, and profession in the life and conduct, against the flatteries and frowns of the world. There must be a day of universal judgment. Happy those who shall have holy boldness before the Judge at that day; knowing he is their Friend and Advocate! Happy those who have holy boldness in the prospect of that day, who look and wait for it, and for the Judge's appearance! True love to God assures believers of God's love to them. Love teaches us to suffer for him and with him; therefore we may trust that we shall also be glorified with him, 2Ti 2:12. We must distinguish between the fear of God and being afraid of him; the fear of God imports high regard and veneration for God. Obedience and good works, done from the principle of love, are not like the servile toil of one who unwillingly labours from dread of a master's anger. They are like that of a dutiful child, who does services to a beloved father, which benefit his brethren, and are done willingly. It is a sign that our love is far from perfect, when our doubts, fears, and apprehensions of God, are many. Let heaven and earth stand amazed at his love. He sent his word to invite sinners to partake of this great salvation. Let them take the comfort of the happy change wrought in them, while they give him the glory. The love of God in Christ, in the hearts of Christians from the Spirit of adoption, is the great proof of conversion. This must be tried by its effects on their temper, and their conduct to their brethren. If a man professes to love God, and yet indulges anger or revenge, or shows a selfish disposition, he gives his profession the lie. But if it is plain that our natural enmity is changed into affection and gratitude, let us bless the name of our God for this seal and earnest of eternal happiness. Then we differ from the false professors, who pretend to love God, whom they have not seen, yet hate their brethren, whom they have seen.