To pretend angels do not exist because they are invisible is to believe we never sleep because we don't see ourselves sleeping.

It is altogether unlawful to kill oneself... Wherefore suicide is contrary to the inclination of nature, and to charity whereby every man should love himself... Life is God's gift to man, and is subject to His power, Who kills and makes to live. Hence whoever takes his own life, sins against God... for it belongs to God alone to pronounce sentence of death and life.

By nature all men are equal in liberty, but not in other endowments.

Devotion is a certain act of the will by which man gives himself promptly to divine service.

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 soul, which is the first principle of life, is not a body, but the act of a body; just as heat, which is the principle of calefaction, is not a body, but an act of a body.

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.