Let us begin with faith, which is the first of all the virtues that exists in the heart of a justified man. Not without reason, does the apostle add "unfeigned" to faith. For faith begins justification, provided it be true and sincere, not false or feigned. The faith of heretics does not begin justification, because it is not true, but false; the faith of bad Catholics does not begin justification, because it is not sincere, but feigned. It is said to be feigned in two ways: when either we do not really believe, but only pretend to believe; or when we indeed believe, but do not live, as we believe we ought to do.
― The Art of Dying Well, Chap III