The Summa Theologica is composed of three parts, each containing sets of questions, within which Thomas Aquinas poses and answers specific theological questions. Aquinas was interested in the relationship between knowledge as revealed by God in contrast to philosophical science, which was assembled incrementally through reason. He believed in salvation and saw that as dependent on the revealed knowledge. Related to this was his understanding of the relationship between faith and rational explanation.
To one who has faith, no explanation is necessary. To one without faith, no explanation is possible.
Although revelation was necessary, it did not mean that each person would fully understand everything in that moment. Belief, for him, was the foundation.
We cannot have full knowledge all at once. We must start by believing; then afterwards we may be led on to master the evidence for ourselves.
Aquinas also conveyed a relativist stance that seems ahead of his time. As a philosopher, he acknowledged the value of free thought and open debate, and encouraged people to respect their opponent’s opinions.
We must love them both, those whose opinions we share and those whose opinions we reject, for both have labored in the search for truth, and both have helped us in finding it.