Justification is the declared purpose of God to regard and treat those sinners who believe in Jesus Christ as if they had not sinned, on the ground of the merits of the Savior. It is not mere pardon. Pardon is a free forgiveness of past offenses. It has reference to those sins as forgiven and blotted out. Justification has respect to the law, and to God’s future dealings with the sinner. It is an act by which God determines to treat him hereafter as righteous—as if he had not sinned. The basis for this is the merit of the Lord Jesus Christ, merit that we can plead as if it were our own. He has taken our place and died in our stead; He has met the descending stroke of justice, which would have fallen on our own heads if He had not interposed. - Albert Barnes

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