"Hence learn the meaning of these expressions in the thirty-second Psalm, "Blessed is he whose transgression is forgiven," and "blessed is the man unto whom the Lord imputeth not iniquity." The first expresses the way in which God in justification pardons past and present sins; and the last, the way in which he forgives the sins, that the justified person afterwards commits: he pardons the first formally, and the last by securing the non-imputation of them.
"From what has been said, the exercised Christian may see how to treat the law as a covenant, when it presents its indictment to his conscience, and demands eternal death. He is to send it to Jesus his responsible Surety, and it cannot refuse to go. He is united to Christ as his glorious Husband, and justified in him: and whatever claim the law may have upon him, he is to refer it to his Husband. It is the husband that pays the debts.
"Hence, we may see the reason why the believer's good works are accepted by God: it is neither for their sake, nor his sake, but for Christ's righteousness' sake; it is because the believer's person is accepted in Christ the Beloved, in whom he is declared righteous. In the covenant of grace, acceptance begins with the person, and passes on to the work."John Colquhoun, Sermon IX - Justification