In this way we can admit not only that there is a partial righteousness in works (as our adversaries maintain), but that they are approved by God as if they were absolutely perfect. If we remember on what foundation this is rested, every difficulty will be solved. The first time when a work begins to be acceptable is when it is received with pardon. And whence pardon, but just because God looks upon us and all that belongs to us as in Christ? Therefore, as we ourselves when ingrafted into Christ appear righteous before God, because our iniquities are covered with his innocence; so our works are, and are deemed righteous, because every thing otherwise defective in them being buried by the purity of Christ is not imputed. Thus we may justly say, that not only ourselves, but our works also, are justified by faith alone. Now, if that righteousness of works, whatever it be, depends on faith and free justification, and is produced by it, it ought to be included under it and, so to speak, made subordinate to it, as the effect to its cause; so far is it from being entitled to be set up to impair or destroy the doctrine of justification. Thus Paul, to prove that our blessedness depends not on our works, but on the mercy of God, makes special use of the words of David, “Blessed is he whose transgression is forgiven, whose sin is covered;” “Blessed is the man unto whom the Lord imputeth not iniquity.” Should any one here obtrude the numberless passages in which blessedness seems to be attributed to works, as, “Blessed is the man that feareth the Lord;” “He that has mercy on the poor, happy is he;” “Blessed is the man that walketh not in the counsel of the ungodly,” and “that endureth temptation;” “Blessed are they that keep judgment,” that are “pure in heart,” “meek,” “merciful,”, they cannot make out that Paul’s doctrine is not true. For seeing that the qualities thus extolled never all so exist in man as to obtain for him the approbation of God, it follows, that man is always miserable until he is exempted from misery by the pardon of his sins. Since, then, all the kinds of blessedness extolled in the Scripture are vain so that man derives no benefit from them until he obtains blessedness by the forgiveness of sins, a forgiveness which makes way for them, it follows that this is not only the chief and highest, but the only blessedness, unless you are prepared to maintain that it is impaired by things which owe their entire existence to it. There is much less to trouble us in the name of righteous which is usually given to believers. I admit that they are so called from the holiness of their lives, but as they rather exert themselves in the study of righteousness than fulfill righteousness itself, any degree of it which they possess must yield to justification by faith, to which it is owing that it is what it is.
—John Calvin, Institutes, 3.17.10 (HT: Jack Miller)