Chapter 19 — Part II: The Sacraments — Penance
Section 46. Their Nature — These three parts belong to that class of parts which are necessary to constitute a whole. The human body is composed of many members, -- -hands, feet, eyes and the various other parts; the want of any one of which makes the body be justly considered imperfect, while if none of them is missing, the body is regarded as perfect. In the same way, Penance is composed of these three parts in such a way that though contrition and confession, which justify man, are alone required to constitute its essence, yet, unless accompanied by its third part, satisfaction, it necessarily remains short of its absolute perfection.