By faith alone...

Therefore, it is necessary that faith alone reconciles and justifies. We do not receive forgiveness of sins through other powers of the Law, or because of these: patience, chastity, obedience toward magistrates, and so on. (Nevertheless, these virtues ought to follow faith.) Therefore, we do not receive forgiveness of sins because of love for God, even though this must follow. Besides this way of speaking is well known. At times we use a word for something and use use the same word for the cause and effects of that thing (synecdoche). For example, in Luke 7:47, Christ says, "Her sins, which are many are forgiven--for she loved much." Christ Himself interprets this when He adds, " Your faith has saved you" (7:50). Christ did not mean that the woman had merited forgiveness of sins by that work of love That is why he adds, "Your faith has saved you." But faith is that which freely obtains God's mercy because of God's Word.
~BOC, AP, V (III), 30-32