Evil denotes the lack of good. Not every absence of good is an evil, for absence may be taken either in a purely negative or in aprivative sense. Mere negation does not display the character of evil, otherwise nonexistents would be evil and moreover, a thing would be evil for not possessing the goodness of something else, which would mean that man is bad for not having the strength of a lion or the speed of a wild goat. But what is evil is privation; in this sense blindness means the privation of sight.
Thomas AquinasA person is disposed to an act of choice by an angel ... in two ways. Sometimes, a man's understanding is enlightened by an angel to know what is good, but it is not instructed as to the reason why ... But sometimes he is instructed by angelic illumination, both that this act is good and as to the reason why it is good.
Thomas AquinasThe soul is like an uninhabited world that comes to life only when God lays His head against us.
Thomas AquinasClearly the person who accepts the Church as an infallible guide will believe whatever the Church teaches.
Thomas AquinasReasoning is compared to understanding as movement is to rest, or acquisition to possession.... Since movement always proceeds from something immovable, and ends in something at rest, hence it is that human reasoning, in the order of inquiry and discovery, proceeds from certain things absolutely understood--namely, the first principles; and, again, in the order of judgment, returns by analysis to first principles, in the light of which it examines what it has found. Now it is clear that rest and movement are not to be referred to different powers, but to one and the same.
Thomas AquinasIt 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.
Thomas Aquinas