LEV. 18:5. Ye shall therefore keep my statutes. Although Moses introduces this passage, where he exhorts the Israelites to cultivate chastity in respect to marriage, and not to fall into the incestuous pollutions of the Gentiles, yet, as it is a remarkable one, and contains general instruction, from whence Paul derives his definition of the righteousness of the Law, (Rom. 10:5,) it seems to me to come in very appropriately here, inasmuch as it sanctions and confirms the Law by the promise of reward. The hope of eternal life is, therefore, given to all who keep the Law; for those who expound the passage as referring to this earthly and transitory life are mistaken.1 The cause of this error was, because they feared that thus the righteousness of faith might be subverted, and salvation grounded on the merit of works. But Scripture does not therefore deny that men are justified by works, because the Law itself is imperfect, or does not give instructions for perfect righteousness; but because the promise is made of none effect by our corruption and sin. Paul, therefore, as I have just said, when he teaches that righteousness is to be sought for in the grace of Christ by faith, (Rom. 10:4,) proves his statement by this argument, that none is justified who has not fulfilled what the Law commands. Elsewhere also he reasons by contrast, where he contends that the Law does not accord with faith as regards the cause of justification, because the Law requires works for the attainment of salvation, whilst faith directs us to Christ, that we may be delivered from the curse of the Law. Foolishly, then, do some reject as an absurdity the statement, that if a man fulfils the Law he attains to righteousness; for the defect does not arise from the doctrine of the Law, but from the infirmity of men, as is plain from another testimony given by Paul. (Rom. 8:3.) We must observe, however, that salvation is not to be expected from the Law unless its precepts be in every respect complied with; for life is not promised to one who shall have done this thing, or that thing, but, by the plural word, full obedience is required of us. The pratings of the Popish theologians about partial righteousness are frivolous and silly, since God embraces at once all the commandments; and who is there that can boast of having thoroughly fulfilled them? If, then, none was ever clear of transgression, or ever will be, although God by no means deceives us, yet the promise becomes ineffectual, because we do not perform our part of the agreement.
—John Calvin, Commentaries on the Four Last Books of Moses Arranged in the Form of a Harmony, trans. Charles William Bingham (repr. Bellingham, WA: Logos Bible Software, 2010), 3.203–05.