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.

The theologian considers sin mainly as an offence against God; the moral philosopher as contrary to reasonableness.

To one who has faith, no explanation is necessary. To one without faith, no explanation is possible.

Arrive at knowledge over small streamlets, and do not plunge immediately into the ocean, since progress must go from the easier to the more difficult.

Hold firmly that our faith is identical with that of the ancients. Deny this, and you dissolve the unity of the Church.

We should love others truly, for their own sakes rather than our own.

If a thing can be done adequately by means of one, it is superfluous to do it by means of several; for we observe that nature does not employ two instruments [if] one suffices.