1 John 5:2

By this we know that we love the children of God, when we love God, and keep his commandments.

By this we know that we are the children God,.... The Ethiopic version reads, "by this know that we love God"; which, in connection with what follows, makes a tautology, and is a proving "idem per idem": whereas the apostle's view is to show when love to the saints is right; and that is,

when we love God, and keep his commandments: love to the brethren may arise from such a cause, as may show that it is not brotherly love, or of a spiritual kind; it may arise from natural relation, or civil friendship, or from a benefit or favour received from them, and from some natural external excellency seen in them; and a man may do acts of love and kindness to the brethren, from what may be called good nature in himself, or with sinister views; but true love to the brethren springs from love to God: such who love the saints aright, and by which they may know they do so, they love them because they themselves love God, and in obedience to his command; they love them because they belong to God, and are the objects of his love; because his grace is wrought in them, and his image stamped upon them.