Thou hast forgiven the iniquity of thy people
Took it from them, and laid it on Christ, who has bore it, and took it away, so as it shall never return more to their destruction; and by the application of his blood it is taken away from their own consciences; for this denotes the manifestation and discovery of forgiveness to themselves; it is a branch of redemption, and is in consequence of it; and is a fruit of the free favour and good will of God through Christ; and it only belongs to the Lord's special people, the people he has taken into covenant with him, and for whose iniquity Christ was stricken:
thou hast covered all their sin;
this is but another phrase for forgiveness, see ( Psalms 32:1 ) , and this is done by the blood and righteousness, and propitiatory sacrifice of Christ, the antitypical mercy seat, the covering of the law and its transgressions, and the people of God from its curse and condemnation; whose sins are so covered by Christ, as not to be seen by the eye of avenging justice, even all of them, not one remains uncovered.
Selah. (See Gill on Psalms 3:2).