In this first section, Aquinas lays the groundwork for his summary of theology by investigating the basis of religious teaching. Aquinas argues that theology, based on faith, is a necessary branch of knowledge, existing alongside branches of knowledge that are grasped through reason alone. Rational (philosophical) knowledge is available only to the few, while all are in need of salvation. Thus, theology, based on divine revelation, is essential. Moreover, there are things in life that surpass the power of reason, and theology deals with these things.

All knowledge has being as its subject. Different branches of knowledge arrive at the same truth by different means. Theology has practical aspects since it deals with moral issues, but it is generally speculative (theoretical) because it approaches these moral issues as they relate to God. Theology is the highest of the sciences because it is founded in the light of divine—and therefore infallible—knowledge. It is the noblest because it deals with the final end and purpose of all things. Theology’s principal subject is God, and so addresses man as he relates to God.

Aquinas asserts that “grace perfects nature” and thus, natural reason “should minister to faith” (8).