John Gill rightly points out, “It is the will and pleasure of Jehovah, that when his dear children are distressed on account of sin, that they should be comforted; and the ministers of Christ are charged to do this. Speak ye comfortably to Jerusalem, to her very heart, and cry unto her that her iniquity is pardoned: for she hath received of the Lord’s hand double for all her sins (Isa. 40:2).
It is the Lord’s work, and his only, it is his act, and deed, to put away sin from his people. Of this, they themselves are sensible; and therefore, under a sense of sin, apply to him for the removal and putting of it away: hence Job says, I have sinned; what shall I do unto thee, O thou Preserver of men?—Why dost thou not pardon my transgression, and take away mine iniquity? (Job 7:21); plainly intimating, that no other could pardon and forgive, or take away his sin, but the Lord himself, against whom he had sinned: and hence David, when he was under a strong and full conviction of the sin he had been guilty of, here referred unto, in the fifty-first Psalm, that penitential Psalm penned on this occasion, entreats, that God would blot out his transgressions, and cleanse him from his sin (Ps.51:1, 2); which is the same thing as in the text, putting away his sin from him. This is the Lord’s act, and his only.” [edited for this post)