He would be guilty of mortal sin, because he exposes himself to the danger of grievously offending God. Hence, before he acts he must lay aside the doubt; and if he has not hitherto done so, he must confess it, at least, as it is before God. But the scrupulous, who have doubts about everything, must follow another rule: they must obey their confessor. When he tells them to conquer their doubts, and to act against scruples, they should obey with exactness; otherwise they will render themselves unable and unfit to perform any spiritual exercise.