This first volume of Saint Thomas Aquinas’s monumental "Summa Theologica" introduces the foundational principles of Christian theology and philosophy. Covering Questions 1 to 26, Aquinas explores the nature and scope of sacred doctrine, the existence and attributes of God, and the concept of the Holy Trinity. He begins by establishing theology as a science rooted in divine revelation, then presents his famous "Five Ways" to prove God’s existence. The volume delves into God’s simplicity, perfection, goodness, infinity, and immutability, before addressing the complex mystery of the Trinity—Father, Son, and Holy Spirit—as distinct yet unified. Written with clarity for beginners yet profound in depth, this volume lays the groundwork for Aquinas’s systematic synthesis of faith and reason.