The adversaries feign that faith is only a knowledge of the history, and therefore teach that it can coexist with mortal sin. Hence they say nothing concerning faith, by which Paul so frequently says that men are justified, because those who are accounted righteous before God do not live in mortal sin. But that faith which justifies is not merely a knowledge of history, [not merely this, that I know the stories of Christ's birth, suffering, etc. (that even the devils know, )] but it is to assent to the promise of God, in which for Christ's sake, the remission of sins and justification are freely offered. [It is the certainty or the certain trust in the heart, when, with my whole heart, I regard the promises of God as certain and true, through which there are offered me, without my merit, the forgiveness of sins, grace, and all salvation, through Christ the Mediator.] And that no one may suppose that it is mere knowledge we will add further: it is to wish and to receive the offered promise of the remission of sins and of justification. [Faith is that my whole heart takes to itself this treasure. It is not my doing, not my presenting or giving, not my work or preparation, but that a heart comforts itself, and is perfectly confident with respect to this, namely, that God makes a present and gift to us, and not we to Him, that He sheds upon us every treasure of grace in Christ.]
And the difference between this faith and the righteousness of the Law can be easily discerned. Faith is the latreia [divine service], which receives the benefits offered by God; the righteousness of the Law is the latreia [divine service] which offers to God our merits. By faith God wishes to be worshiped in this way, that we receive from Him those things which He promises and offers.
Now, that faith signifies, not only a knowledge of the history, but such faith as assents to the promise, Paul plainly testifies when he says, Rom. 4, 16: Therefore it is of faith, to the end the promise might be sure. For he judges that the promise cannot be received unless by faith. Wherefore he puts them together as things that belong to one another, and connects promise and faith. [There Paul fastens and binds together these two, thus: Wherever there is a promise faith is required and conversely, wherever faith is required there must be a promise.] Although it will be easy to decide what faith is if we consider the Creed where this article certainly stands: The forgiveness of sins. Therefore it is not enough to believe that Christ was born, suffered, was raised again, unless we add also this article, which is the purpose of the history: The forgiveness of sins. To this article the rest must be referred, namely, that for Christ's sake, and not for the sake of our merits, forgiveness of sins is given us. For what need was there that Christ was given for our sins if for our sins our merits can make satisfaction?
As often, therefore, as we speak of justifying faith, we must keep in mind that these three objects concur: the promise, and that, too, gratuitous, and the merits of Christ, as the price and propitiation. The promise is received by faith; the "gratuitous" excludes our merits, and signifies that the benefit is offered only through mercy; the merits of Christ are the price, because there must be a certain propitiation for our sins. Scripture frequently implores mercy, and the holy Fathers often say that we are saved by mercy. As often, therefore, as mention is made of mercy, we must keep in mind that faith is there required, which receives the promise of mercy. And, again, as often as we speak of faith, we wish an object to be understood, namely, the promised mercy. For faith justifies and saves, not on the ground that it is a work in itself worthy, but only because it receives the promised mercy.
And throughout the prophets and the psalms this worship, this latreia, is highly praised, although the Law does not teach the gratuitous remission of sins. But the Fathers knew the promise concerning Christ that God for Christ's sake wished to remit sins. Therefore, since they understood that Christ would be the price for our sins, they knew that our works are not a price for so great a matter [could not pay so great a debt]. Accordingly, they received gratuitous mercy and remission of sins by faith, just as the saints in the New Testament. Here belong those frequent repetitions concerning mercy and faith, in the psalms and the prophets, as this, Ps. 130, 3 sq.: If Thou Lord, shouldest mark iniquities, O Lord, who shall stand? Here David confesses his sins and does not recount his merits. He adds; But there is forgiveness with Thee. Here he comforts himself by his trust in God's mercy, and he cites the promise: My soul doth wait and in His Word do I hope, i.e., because Thou hast promised the remission of sins, I am sustained by this Thy promise. Therefore the fathers also were justified, not by the Law but by the promise and faith. And it is amazing that the adversaries extenuate faith to such a degree, although they see that it is everywhere praised as an eminent service, as in Ps. 50, 15: Call upon Me in the day of trouble: I will deliver thee. Thus God wishes Himself to be known, thus He wishes Himself to be worshiped, that from Him we receive benefits, and receive them, too, because of His mercy, and not because of our merits. This is the richest consolation in all afflictions [physical or spiritual, in life or in death as all godly persons know]. And such consolations the adversaries abolish when they extenuate and disparage faith, and teach only that by means of works and merits men treat with God [that we treat with God, the great Majesty, by means of our miserable, beggarly works and merits].