The Summa Theologica is the masterwork of medieval theologian St. Thomas Aquinas. Written between 1265 and 1274, it was designed to be a comprehensive guide to the main theological teachings of the Catholic Church and has been hailed as a landmark in the history of philosophy.
Thomas Aquinas (1225-1274) was a Dominican priest honored as one of the Doctors of the Catholic Church. He studied and taught at the University of Paris. The book, although unfinished at the time of Aquinas' death, is divided into three sections.
Part one, Prima Pars, is the Theological section and considers the existence of God and nature, labeled God the first cause of the universe and detailing Aquinas' fivefold proof for God's existence. When discussing the Trinity, Aquinas largely follows Augustine of Hippo. Man, the opposite of god, has an intellect and a will.
Part two, Prima Secundae, deals with Ethics and is subdivided into two sections. Both consist of numerous questions that Aquinas then answers. According to Aquinas, human beings acquire morality through habit, and evil results from a deviation from moral law.
Part three, Tertia Pars, details man's journey to God through Christ. The various sacraments are explained, the purpose of them to infuse God's grace into sinful human beings. They are the instruments through which Christ operates.