Hence, also, we see the error of those who, in comparing the Law with the Gospel, represent it merely as a comparison between the merit of works, and the gratuitous imputation of righteousness. This is indeed a contrast not at all to be rejected. For Paul often means by the term “law” the rule of righteous living by which God requires of us what is his own, giving us no hope of life unless we completely obey him, and adding on the other hand a curse if we deviate even in the slightest degree. This Paul does when he contends that we pleasing to God through grace and accounted righteous through his pardon, because nowhere is found that observance of the law for which the reward has been promised. Paul therefore justly makes contraries of the righteousness of the law and that of the gospel.
John Calvin, Institutes of the Christian Religion, 2.9.4