What is the Summa Theologica?
"Written from 1265—1273, the Summa Theologica (or Summa Theologiae, or sometimes referred to as the Summa) is the name of the philosophical summary (summa) of the theology (theologica) of the Roman Catholic Church as presented and organized by Thomas Aquinas, 1225—1274.
Aquinas used Aristotelian philosophy as a framework for the Summa Theologica, believing Aristotle to be a friend of Christianity when many earlier thinkers had seen him as a foe. Aquinas, however, did reject Aristotle’s concept of a detached and distant God in favor of the God of the Bible who is intensely interested and knowable. The Summa Theologica was declared to be the official teaching of the Roman Catholic Church by Pope Leo XIII (1879).
The Summa Theologica is divided into three parts. The first part covers the nature of God, creation, angels, man, and divine government (sovereignty). The second part addresses ethics, habits, law, faith, wisdom, self-control, morality, prophecy, miracles, and the contemplative life. The third part instructs the reader on the doctrine of Christ including His incarnation, life, death, and resurrection. In the same section, Aquinas addresses the need for sacraments in the remission of sins. A majority of the third section is devoted to explaining the sacraments..." from the article: What is the Summa Theologica?
Summa Theologiae (complete text link from Aquinas Institute)
Aquinas Institute (website link)