Summa contra Gentiles3.143 Chapter CXLIII. Of the punishment due to mortal and venial sin in relation to the last end

It is clear from what has been said, that sin may happen in two ways. In one way, so that the intention of the mind altogether breaks away from its order to God, who is the last end of the good: and this is mortal sin. In another way, so that, without prejudice to the human mind’s order to its last end, some obstacle is placed, whereby it is hampered in tending freely to its end: and this is called venial sin. If, then, punishments must differ according to the difference of sins, it follows that he who sins mortally, should be punished so as to forfeit man’s end: but that he who sins venially, should be punished not to the extent of forfeiting it, but so as to be hampered, or experience difficulty, in obtaining the end. For thus is the equality of justice maintained: so that in the same way that man by sinning voluntarily turns aside from his end, so by way of punishment, against his will, should he be hindered in the attainment of his end.

Again. The will in man corresponds to the natural inclination in natural things. Now, if a natural thing be deprived of its natural inclination to its end, it is quite unable to reach that end: thus a heavy body, if it lose its weight by corruption, and becomes light, will never reach the centre. Whereas if it be hindered in its movement, while retaining its inclination to the end, it will reach its end, when the obstacle is removed. When a man sins mortally, the intention of his will is altogether turned away from his last end: whereas, when he sins venially, his intention remains turned towards his end, yet somewhat hampered, by reason of his adhering more than he ought, to those things that are directed to the end. Consequently the punishment due to one who sins mortally is that he be altogether debarred from obtaining his end; while the punishment due to one who sins venially, is that he experience difficulty before attaining his end.

Moreover. When a man gets a good thing unintentionally, this is by luck and chance. If, then, a man whose intention is turned away from his last end, obtains that last end, it will be by luck and chance. But this is unreasonable. Because the last end is a good of the intelligence: whereas luck is incompatible with intelligence: since things that happen by chance, occur without the bidding of the intellect. And it is unreasonable that the intellect obtain its end otherwise than in an intelligent way. Therefore a man who, by sinning mortally, has his intention turned away from his last end, will not obtain his last end.

Again. Matter does not receive a form from the agent unless it be disposed to that form. Now the end and the good are the perfection of the will, as form is of matter. Consequently the will does not obtain the last end, unless it be fittingly disposed. But the will is disposed to the end by intending and desiring the end. Therefore a man will not obtain his end if his intentions be averted from the end.

Moreover. In things ordained to an end, we find that if the end is or will be obtained, we must of necessity presuppose the things required for obtaining it: and if those things be not granted, neither will the end be obtained: for if the end can be obtained without the things directed to the end, it is useless to seek the end by such means. Now, all are agreed that man obtains his last end, which is beatitude, by deeds of virtue, the chief of which is the intention of the right end. Therefore, if a man act against virtue, through turning away from the intention of the last end, it is fitting that he be deprived of his last end.

Hence it is said (Matth. vii. 23): Depart from Me, all you that work iniquity.