Will not impute sin - On whom the Lord will not charge his sins; or who shall not be reckoned or regarded as guilty. This shows clearly what the apostle meant by imputing faith without works. It is to pardon sin, and to treat with favor; not to reckon or charge a man's sin to him; but to treat him, though personally undeserving and ungodly Romans 4:5, as though the sin had not been committed. The word "impute" here is used in its natural and appropriate sense, as denoting to charge on man what properly belongs to him. See the note at Romans 4:3.

Blessed is the man to whom the Lord will not impute sin - That man is truly happy to whose charge God does not reckon sin; that is, they alone are happy who are redeemed from the curse of the law and the consequence of their ungodly life, by having their sins freely forgiven, through the mercy of God.

Blessed is the man to whom the Lord will not impute sin. As he does not to those whom he justifies in Christ, and by his righteousness; for the sins of such he has imputed to his Son, as their surety; and he has bore them, took them away, having made full satisfaction for them; so that these persons will never be charged with them: they now appear before the throne without fault, and are blameless and irreproveable in the sight of God, and therefore must be eternally happy; for he will never think of their sins any more to their hurt; he will remember them no more; he "will never reckon them to them", but acquit them from them, justify and accept them; wherefore they must be secure from wrath and condemnation, enjoy much peace and comfort now, and be happy hereafter.