Verse 10. - The question whether "in this" ἐν τούτῳ refers to what precedes or to what follows is here unimportant, for both are similar in meaning; and "in this" may refer to both. "By their fruits ye shall know them." The children of God do righteousness, and not sin; the children of the devil do sin, and not righteousness. Of course, moral parentage is meant in both cases. Nothing here lends any countenance to the view that the writer is a dualist and inculcates two principles of existence - God and the devil. All, whether good or bad, are God's creatures (John 1:3); but while all are his children by creation, some become his children spiritually also, while others become the children of Satan. St. John's "teaching about the devil is not at all agreeable to those who dwell exclusively on the sunny aspects of the world and of life, and would shut their eyes to what is dark and terrible. They like to hear of a Being who is all-gracious and loving; the vision of one who is the enemy of all that is gracious and loving shocks them - they wish to suppose that it belongs to the world's infancy, and that it disappears as we know more" (Maurice). The expression, "the children of the devil," must not be confounded with the Hebraistic expressions, "children of perdition, children of darkness," "children of light, son of death," "son of perdition," etc. As so often, St. John not only restates the case in a new form, but adds a new thought to it - he that loveth not his brother. This forms the link with the next section (verses 13-24), on brotherly love. Of all failures in doing righteousness this is the most conspicuous - failing to love one's brother. And who is my brother? The answer is the same as to the question, "And who is my neighbour?" Mankind at large. The meaning cannot be limited to the children of God. Even τοὺς ἀδελφούς (verses 14, 16) does not exclude unbelievers, still less does τὸν ἀδελφὸν αὐτοῦ. This is confirmed:

(1) By the fact that the opposite case (verse 13) is the children of the world hating Christians; the true opposite of Christians loving Christians would be the children of the world hating one another.

(2) By the cited example of Christ (verse 16), who died for us when we were aliens from God. Of course, if the Christian must love all men, a fortiori he must love Christians.

3:3-10 The sons of God know that their Lord is of purer eyes than to allow any thing unholy and impure to dwell with him. It is the hope of hypocrites, not of the sons of God, that makes allowance for gratifying impure desires and lusts. May we be followers of him as his dear children, thus show our sense of his unspeakable mercy, and express that obedient, grateful, humble mind which becomes us. Sin is the rejecting the Divine law. In him, that is, in Christ, was no sin. All the sinless weaknesses that were consequences of the fall, he took; that is, all those infirmities of mind or body which subject man to suffering, and expose him to temptation. But our moral infirmities, our proneness to sin, he had not. He that abides in Christ, continues not in the practice of sin. Renouncing sin is the great proof of spiritual union with, continuance in, and saving knowledge of the Lord Christ. Beware of self-deceit. He that doeth righteousness is righteous, and to be a follower of Christ, shows an interest by faith in his obedience and sufferings. But a man cannot act like the devil, and at the same time be a disciple of Christ Jesus. Let us not serve or indulge what the Son of God came to destroy. To be born of God is to be inwardly renewed by the power of the Spirit of God. Renewing grace is an abiding principle. Religion is not an art, a matter of dexterity and skill, but a new nature. And the regenerate person cannot sin as he did before he was born of God, and as others do who are not born again. There is that light in his mind, which shows him the evil and malignity of sin. There is that bias upon his heart, which disposes him to loathe and hate sin. There is the spiritual principle that opposes sinful acts. And there is repentance for sin, if committed. It goes against him to sin with forethought. The children of God and the children of the devil have their distinct characters. The seed of the serpent are known by neglect of religion, and by their hating real Christians. He only is righteous before God, as a justified believer, who is taught and disposed to righteousness by the Holy Spirit. In this the children of God are manifest, and the children of the devil. May all professors of the gospel lay these truths to heart, and try themselves by them.In this the children of God are manifest,.... By regenerating grace, and not sinning, in the sense before explained, in consequence of it: adoption is an act of God's grace and sovereign will; it is secret in his own heart, and is secured in divine predestination, and in the covenant of grace, and is antecedent to regeneration: regeneration and faith do not make men the children of God, but manifest them to be so; adoption makes them the children of God, and entitles them to the inheritance; regeneration gives them the nature of the children of God, and makes them meet for it, and manifests their right unto it; not to the men of the world, but to themselves and other saints:

and the children of the devil; such as imitate him, do his will and his lusts, and are openly under his power and influence; these are distinguishable from regenerate persons, and the children of God, by their lives and conversations; so the people of the nations of the world are called, "the children of Samael", and the serpent, by the Jews (m), which are with them the names of the devil.

Whosoever doth not righteousness is not of God: that is, he does; not appear to be born of God, who does not by faith lay hold on the righteousness of Christ for his justification before God, and acceptance with him; and who does not do works of righteousness in faith from a principle of love, and with a view to the glory of God; for where regenerating grace is, there will be such graces and such practices:

neither he that loveth not his brother; for as he that loveth God, and Christ, and the brethren, appears manifestly to be born again, and to have passed from death to life, so he that does not is in darkness, in a state of unregeneracy, and walks and continues therein; for was he born again, he would be taught of God to love the saints; see 1 John 4:7.

(m) Raya Mehimna in Zohar in Lev. fol. 34. 2.