Having laid down several motives to brotherly love before, by way of excitation, as an help to their affections, he comes now to propound some directions to them as an help to their endeavours.
And the first is this, to take special care that their love be sincere, and not hypocritical. Let us not love in word, that is, in word only, but in deed, and in truth. As if he had said, "Let our deeds speak the truth of our love; sincere love is fruitful; true affection will put forth itself into action; it doth not rest at the tongue's end, but will be seen at the finger's end, rendering us laborious in works and offices of friendship; as faith, so love without works is dead; and as faith is justified by works, so is our love also.
Observe next, The encouragement which our apostle gives to the exercise of this true love, hereby we shall know that we are of the truth, and shall assure our hearts before him: That is, "By such efficacy and real fruits of our love we shall know that we are true Christians, who live by, and walk according to the rule of the gospel, which is emphatically stiled the truth, and shall have the assured testimony of our consciences, that we are sincere in the sight of God."
Learn hence, 1. That the love of Christians one to another ought not to be verbal, or in word only, but in deed, and in truth.
2. That the sincerity of our love to our brethren is the security of our consciences and estates before God. A Christian may be assured of his good estate, and may build his assurance upon the sincerity of his love to God and Christians.