Matthew Henry 1 John 1:9

If we confess our sins, v. 9. Penitent confession and acknowledgment of sin are the believer’s business, and the means of his deliverance from his guilt. And, 2. His encouragement thereto, and assurance of the happy issue. This is the veracity, righteousness, and clemency of God, to whom he makes such confession: He is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness, v. 9. God is faithful to his covenant and word, wherein he has promised forgiveness to penitent believing confessors. He is just to himself and his glory who has provided such a sacrifice, by which his righteousness is declared in the justification of sinners. He is just to his Son who has not only sent him for such service, but promised to him that those who come through him shall be forgiven on his account. By his knowledge (by the believing apprehension of him) shall my righteous servant justify many, Isa. 53:11. He is clement and gracious also, and so will forgive, to the contrite confessor, all his sins, cleanse him from the guilt of all unrighteousness, and in due time deliver him from the power and practice of it.