Thomas Aquinas was born in 1225 at his family’s castle of Roccasecca in the kingdom of Naples. His uncle was abbot of the Benedictine monastery at Monte Cassino and it was expected that Thomas would assume that position in time.
Aquinas began his early education at the monastery and left at 16 to attend the University of Naples. At university, Aquinas came under the influence of the Dominicans, who were actively recruiting the best young scholars in the universities.
Aquinas lived at an important time in the history of the Catholic Church. The works of Aristotle had been rediscovered and were becoming widely available in Latin and creating fervent debates among scholars. The Dominican and Franciscan monastic orders had also arrived on the scene to challenge the existing established clerical orders of early Medieval Europe.
Initially Aquinas’ desire to join the Dominican order resulted in him being kidnapped by his brothers and he was held captive for two years. Eventually, it took the intervention of Pope Innocent IV to allow him to leave and join the order.
In late 1244, Aquinas was sent to the Dominican school in Cologne, where Albertus Magnus was lecturing on philosophy and theology. The following year, Aquinas accompanied Albertus to the University of Paris, where they remained for three years.
Thomas obtained his doctorate the University of Paris, an institution that had been created by the unification of the monastic schools on the Left Bank and the cathedral school at Notre Dame. In a controversial ongoing debate Aquinas defended the mendicant orders and, of greater historical importance, countered the Franciscan tendency to reject Greek philosophy.
Aquinas began his career teaching in Paris, Bologna and Rome and spent many years lecturing and writing. He traveled Europe attending philosophical debates and acted as an advisor to the King of France and the pope. He also worked diligently on his great literary work, the Summa Theologica. The church offered to make him archbishop of Naples and abbot of Monte Cassino, but he refused both.
In 1274, Pope Gregory X directed Aquinas to attend the Second Council of Lyons ostensibly negotiate a resolution to the differences between the Greek and Latin churches. Along the way, he stopped at the castle of a niece but became seriously ill. Aquinas desired to end his days in a monastery but was unable to reach a Dominican institution and was taken to the Cistercian monastery of Fossa Nuova. After a lingering illness of seven weeks, Aquinas died on March 7, 1274
Aquinas was canonized by the Catholic Church in 1323.
Only Augustine of Hippo is considered to have had as much influence on Catholic Church teaching. Pope Leo XIII, in 1879 stated that Aquinas's theology was a definitive exposition of Roman Catholic doctrine and that all clergy were to take the teachings of Aquinas as the basis of their theological positions.

Summa Theologica

The Summa Theologica or the Theological Summary is an attempt to describe the relationship between God and man and explain the role of Jesus Christ in the reconciliation of both. Aquinas cites proofs of the existence of God and attempts to describe the nature of the divine.
The book is divided into three parts. Part One deals primarily with God and presents 119 questions concerning the existence and nature of God, the Creation, angels, the work of the six days of Creation, the essence and nature of man, and divine government. Part Two discusses 303 questions concerning the purpose of man, habits, law, vices, temperance and virtues, the nature of justice, the concept of grace, and the religious versus the secular life. Part three concerns Christ and addresses 90 questions concerning the life and teachings of Christ and the importance of Christ’s Resurrection.
In some editions of the Summa Theologica there are an additional 99 questions concerning issues like excommunication, indulgences, confession, marriage, purgatory, and the role of the saints. Scholars believe that Rainaldo da Piperno, a friend of Aquinas, probably gathered the material from various lectures.
Radically, Aquinas adopted Aristotelian ideas, to explain the origin, operation, and purpose of the entire universe. The resulting The Summa Theologica expresses Aquinas’s belief that theology can be expressed and codified in a comprehensive and rational system.
Aquinas also uses the language and concepts of philosophy to examine the existence of God, the nature and limits of human knowledge, and the purpose of man. Aquinas’s enlistment of Aristotelian precepts reveals Aquinas to be an open minded medieval thinker. Aquinas, again channeling Aristotle, believed that every human being, regardless of his or her beliefs, shares in humanity through the possession and use of reason and that reason is the essential quality of humanity.