3. A glance at one’s own righteousness provides no peace for the conscience

Now if we ask in what way the conscience can be made quiet before God, we shall find the only way to be that unmerited righteousness be conferred upon us as a gift of God. Let us ever bear in mind Solomon’s question: “Who will say, ‘I have made my heart clean; I am pure from my sin’?” [Prov. 20:9]. Surely there is no one who is not sunken in infinite filth! Let even the most perfect man descend into his conscience and call his deeds to account, what then will be the outcome for him? Will he sweetly rest as if all things were well composed between him and God and not, rather, be torn by dire torments, since if he be judged by works, he will feel grounds for condemnation within himself? The conscience, if it looks to God, must either have sure peace with his judgment or be besieged by the terrors of hell. Therefore we profit nothing in discussing righteousness unless we establish a righteousness so steadfast that it can support our soul in the judgment of God. When our souls possess that by which they may present themselves fearless before God’s face and receive his judgment undismayed, then only may we know that we have found no counterfeit righteousness. The apostle, then, with good reason strongly insists on this point. I prefer to express it in his words rather than mine.  “If the promise of the inheritance comes from the law, faith is nullified and the promise is void.” [Rom. 4:14, cf. Vg.] He first infers that faith has been nullified and canceled if the promise of righteousness looks to the merits of our works, or depends upon the observance of the law. For no one can ever confidently trust in it because no one will ever come to be really convinced in his own mind that he has satisfied the law, as surely no one ever fully satisfies it through works.

~John Calvin, Institutes, 3.13.3.