This foundational work of scholastic theology systematically investigates the nature and existence of God, setting out from the premise that the human mind can attain knowledge of the divine through its sensible effects. The argument opens by establishing that sacred doctrine constitutes a true science based upon revealed principles, transcending mere philosophy while harmonizing reason with faith. Aquinas methodically proves the existence of God through five distinct cosmological and teleological pathways, moving from motion, efficient causation, contingency, gradation, and cosmic governance to the necessary first cause. Having established that God exists, the text proceeds into a rigorous negative theology, defining the divine essence by what it is not.
Aquinas demonstrates that God is altogether simple, lacking any composition of matter and form, essence and existence, or genus and difference. Because God is pure act without potentiality, He is absolute being itself, infinite, immutable, and eternal. Every created perfection—whether goodness, wisdom, or power—pre-exists in God in a more eminent manner as in their supreme and universal cause. The work further explores how God is present in all things through essence, presence, and power, not as a constituent part, but as an agent present to its effect. Finally, the text addresses the human capacity to know God, concluding that while created intellects cannot comprehend the infinite divine essence naturally, they may attain true analogical knowledge through creatures and, ultimately, through the light of grace.
