Thomas Aquinas

“ Wherefore a sin is aggravated by the very fact that it is committed through certain malice, and so much the more, as the malice is greater; whereas it is diminished by being committed through passion, and so much the more, as the passion is stronger. Secondly, because the passion which incites the will to sin, soon passes away, so that man repents of his sin, and soon returns to his good intentions; whereas the habit, through which a man sins, is a permanent quality, so that he who sins through malice, abides longer in his sin. ”

“ Again, the consequence of loving a thing less is that one chooses to suffer some hurt in its regard, in order to obtain a good that one loves more: as when a man, even knowingly, suffers the loss of a limb, that he may save his life which he loves more. ”

“ Now to revolt from God is to sin. Therefore some sin purposely or through certain malice.
I answer that, Man like any other being has naturally an appetite for the good; and so if his appetite incline away to evil, this is due to corruption or disorder in some one of the principles of man: for it is thus that sin occurs in the actions of natural things. ”

“ To do an action as an unjust man does, may be not only to do unjust things through certain malice, but also to do them with pleasure, and without any notable resistance on the part of reason, and this occurs only in one who has a habit.
Reply to Objection 2: It is true that a man does not fall suddenly into sin from certain malice, and that something is presupposed ”

“ Secondly, the will, of its own accord, may tend to an evil, through the removal of some obstacle: for instance, if a man be prevented from sinning, not through sin being in itself displeasing to him, but through hope of eternal life, or fear of hell, if hope give place to despair, or fear to presumption, he will end in sinning through certain malice, being freed from the bridle, as it were. ”

“ The malice through which anyone sins, may be taken to denote habitual malice, in the sense in which the Philosopher (Ethic. v, 1) calls an evil habit by the name of malice, just as a good habit is called virtue: and in this way anyone is said to sin through malice when he sins through the inclination of a habit. ”

“ Evil cannot be intended by anyone for its own sake; but it can be intended for the sake of avoiding another evil, or obtaining another good, as stated above: and in this case anyone would choose to obtain a good intended for its own sake, without suffering loss of the other good; even as a lustful man would wish to enjoy a pleasure without offending God ”

“ Accordingly when an inordinate will loves some temporal good, e.g. riches or pleasure, more than the order of reason or Divine law, or Divine charity, or some such thing, it follows that it is willing to suffer the loss of some spiritual good, so that it may obtain possession of some temporal good. ”