The things that we love tell us what we are.

It may well happen that what is in itself the more certain on account of the weakness of our intelligence, which is dazzled by the clearest objects of nature; as the owl is dazzled by the light of the sun. Hence the fact that some happen to doubt about articles of faith is not due to the uncertain nature of the truths, but to the weakness of human intelligence; yet the slenderest knowledge that may be obtained of the highest things is more desirable than the most certain knowledge obtained of lesser things...

...[sacred] doctrine is especially based upon arguments from authority, inasmuch as its principles are obtained by revelation: thus we ought to believe on the authority of those to whom the revelation has been made. Nor does this take away from the dignity of this doctrine, for although the argument from authority based on human reason is the weakest, yet the argument from authority based on divine revelation is the strongest.

It is clear that he does not pray, who, far from uplifting himself to God, requires that God shall lower Himself to him, and who resorts to prayer not to stir the man in us to will what God wills, but only to persuade God to will what the man in us wills.

Sacred Scripture, since it has no science above itself, can dispute with one who denies its principles only if the opponent admits some at least of the truths obtained through divine revelation; thus we can argue with heretics from texts in Holy Writ, and against those who deny one article of faith we can argue from another. If our opponent believes nothing of divine revelation, there is no longer any means of proving the articles of faith by reasoning, but only of answering his objections - if he has any - against faith.

Man can sin against nature in two ways. First, when he sins against his specific rational nature, acting contrary to reason. In this sense, we can say that every sin is a sin against man's nature, because it is against man's right reason....

Secondly, man sins against nature when he goes against his generic nature, that is to say, his animal nature. Now, it is evident that, in accord with natural order, the union of the sexes among animals is ordered towards conception. From this it follows that every sexual intercourse that cannot lead to conception is opposed to man's animal nature.

If all the sins of the flesh are worthy of condemnation because by them man allows himself to be dominated by that which he has of the animal nature, much more deserving of condemnation are the sins against nature by which man degrades his own animal nature....

Given the sin of impiety through which they [the Romans] sinned against the divine nature [by idolatry], the punishment that led them to sin against their own nature followed.... I say, therefore, that since they changed into lies [by idolatry] the truth about God, He brought them to ignominious passions, that is, to sins against nature; not that God led them to evil, but only that he abandoned them to evil....