Which questions about God did St. Anselm of Canterbury try to answer through reason?

St. Anselm of Canterbury sought to provide rational foundations for core tenets of Christian faith, primarily focusing on the existence of God and the necessity of the Incarnation.

The Existence of God

Anselm aimed to prove God's existence through reason alone, independent of scriptural authority. In his work Monologion, he presented three proofs based on Neoplatonic thought, which move from the observation of multiplicity in the world—such as various good things or beings of varying perfection—to the existence of a single, supremely good and perfect source: God.12

In his later work, the Proslogion, he formulated the ontological argument. He argued that the very concept of God as "that than which nothing greater can be conceived" necessitates God's existence. He reasoned that if such a being existed only in the mind, it would not be the greatest possible being, as a being that exists in both reality and the mind is greater.312

The Necessity of the Incarnation

In his work Cur Deus homo ("Why God Became Man"), Anselm used reason to explain why it was necessary for God to become human to achieve atonement. He argued that human sin offended God's infinite righteousness, requiring a satisfaction that only a being who was both God and human could provide.45