There are many different kinds of sin. It is possible by a single act to commit more than one sin. And a given sin may be repeated any number of times. To get the exact number of our misdeeds we must begin by counting as many sins at least as there are kinds of sin. We might say there is an offense for every time a commandment or precept is violated, for sin is a transgression of the law. But this would be insufficient inasmuch as the law may command or forbid more than one thing.Let the first commandment serve as an example.
It is broken by sins against faith, or unbelief, against hope, or despair, against charity, against religion, etc. All these offenses are specifically different, that is, are different kinds of sin; yet but one precept is transgressed. Since therefore each commandment prescribes
the practice of certain virtues, the first rule is that there is a sin for every virtue violated. But this is far from exhausting our capacity for evil. Our virtue may impose different obligations, so that against it alone we may offend in many different ways. Among the virtues prescribed by the first commandment is that of religion, which concerns the exterior homage due to God. I may worship false gods, thus offending against the virtue of religion, and commit a sin of idolatry. If I offer false homage to the true God, I also violate the virtue of religion, but commit a sin specifically different, a sin of superstition. Thus these different offenses are against but one of several virtues enjoined by one commandment. The virtue of charity is also prolific of obligations; the virtue of chastity even more so. One act against the latter may contain a four-fold malice. It would be out of place here to adduce more examples: a detailed treatment of the virtues and commandments will make things clearer. For the moment it is necessary and sufficient to know that a commandment may prescribe many virtues, a virtue may impose many obligations, and there is a specifically different sin for each obligation violated. But we can go much farther than this in wrongdoing, and must count one sin every time the act is committed.
"Yes, but how are we to know when there is one act or more than one act! An act may be of long or short duration. How many sins do I commit if the act lasts, say, two hours? And how can I tell where one act ends and the other begins ?" In an action which endures an hour or two hours, there may be one and there may be a dozen acts. When the matter a sinner is working on is a certain, specified evil, the extent to which he prevaricates numerically depends upon the action of the will. A fellow who enters upon the task of slaying his neighbor can kill but once in fact; but he can commit the sin of murder in his soul once or a dozen times. It depends on the will. Sin is a deliberate transgression, that is, first of all an act of the will. If he resolves once to kill and never retracts till the deed of blood is done, he sins but once. If he disavows his resolution and afterwards resolves anew, he repeats the sin of murder in his soul as often as he goes through this process of will action. This sincere retraction of a deed is called moral interruption and it has the mysterious power of multiplying sins.
Not every interruption is a moral one. To put the matter aside for a certain while in the hope of a better opportunity, for the procuring of necessary facilities or for any other reason, with the unshaken purpose of pursuing the course entered upon, is to suspend action; but this action is wholly exterior, and does not affect the will. The act of the will perseveres, never loses its force, so there is no moral, but only a physical, interruption. There is no renewal of consent for it has never been withdrawn. The one moral act goes on, and but one sin is committed. Thus, of two wretches on the same errand of crime, one may sin but once, while the other is guilty of the same sin a number of times. But the several sins last no longer than the one. Which is the more guilty ? That is a question for God to decide; He does the judging, we do the counting. This possible multiplication of sin where a single act is apparent emphasizes the fact that evil and good proceed from the will. It is by the will primarily and essentially that we serve or offend God, and, absolutely speaking, no exterior deed is necessary for the accomplishment of this end.
The exterior deed of sin always supposes a natural preparation of sin—thought, desires, resolution,—which precede or accompany the deed, and without which there would be no sin. It is sinful only inasmuch as it is related to the will and is the fruit thereof. The interior act constitutes the sin in its being; the exterior act constitutes it in its completeness. All of which leads up to the conclusion, of a nature perhaps to surprise some, that to resolve to sin and to commit the sin in deed are not two different sins, but one complete sin, in all the fullness of its malice. True, the exterior act may give rise to scandal, and from it may devolve upon us obligations of justice, the reparation of injury done; true, with the exterior complement the sin may be more grievous. But there cannot be several sins if there be one single uninterrupted act of the will.
An evil thing is proposed to your mind; you enjoy the thought of doing it, knowing it to be wrong; you desire to do it and resolve to do it; you take the natural means of doing it; you succeed and consummate the evil—a long drawn out and well prepared deed, 'tis true, but only one sin. The injustices, the scandal, the sins you might commit incidentally, which do not pertain naturally to the deed, all these are another matter, and are other kinds of sins; but the act itself stands alone, complete and one. But these interior acts of sin, whether or not they have reference to external completion, must be sinful. The first stage is the suggestion of the imagination or simple seeing of the evil in the mind, which is not sinful; the next is the moving of the sensibility or the purely animal pleasure experienced, in which there is no evil, either; for we have no sure mastery over these faculties. From the imagination and sensibility the temptation passes before the will for consent. If consent is denied, there is no deadly malice or guilt, no matter how long the previous effects may have been endured. No thought is a sin unless it be fully consented to.
Source: Moral Briefs by Rev. John H. Stapleton, Imprimatur 1904