5. See how our works lie under the curse of the law if they are tested by the standard of the law. But how can unhappy souls set themselves with alacrity to a work from which they cannot hope to gain any thing in return but cursing? On the other hand, if freed from this severe exaction, or rather from the whole rigor of the law, they hear themselves invited by God with paternal levity, they will cheerfully and alertly obey the call, and follow his guidance. In one word, those who are bound by the yoke of the law are like servants who have certain tasks daily assigned them by their masters. Such servants think that nought has been done; and they dare not come into the presence of their masters until the exact amount of labour has been performed. But sons who are treated in a more candid and liberal manner by their parents, hesitate not to offer them works that are only begun or half finished, or even with something faulty in them, trusting that their obedience and readiness of mind will be accepted, although the performance be less exact than was wished. Such should be our feelings, as we certainly trust that our most indulgent Parent will approve our services, however small they may be, and however rude and imperfect. Thus He declares to us by the prophet, “I will spare them as a man spareth his own son that serveth him,” (Mal. 3:17); where the word spare evidently means indulgence, or connivance at faults, while at the same time service is remembered. This confidence is necessary in no slight degree, since without it every thing should be attempted in vain; for God does not regard any sock of ours as done to himself, unless truly done from a desire to serve him. But how can this be amidst these terrors, while we doubt whether God is offended or served by our work?
6. This is the reason why the author of the Epistle to the Hebrews ascribes to faith all the good works which the holy patriarchs are said to have performed, and estimates them merely by faith (Heb. 11:2). In regard to this liberty there is a remarkable passage in the Epistle to the Romans, where Paul argues, “Sin shall not have dominion over you; for ye are not under the law, but under grace,” (Rom. 6:14). For after he had exhorted believers, “Let not sin therefore reign in your mortal body, that ye should obey it in the lusts thereof: Neither yield ye your members as instruments of unrighteousness unto sin; but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God;” they might have objected that they still bore about with them a body full of lust, that sin still dwelt in them. He therefore comforts them by adding, that they are freed from the law; as if he had said, Although you feel that sin is not yet extinguished, and that righteousness does not plainly live in you, you have no cause for fear and dejection, as if God were always offended because of the remains of sin, since by grace you are freed from the law, and your works are not tried by its standard. Let those, however who infer that they may sin because they are not under the law, understand that they have no right to this liberty, the end of which is to encourage us in well-doing.
– John Calvin, Institutes, Book 3, Ch 19, par 5-6, taken from ccel.org on 2019/11/03