What theological concept did Anselm contribute to the understanding of God?

Anselm's significant contribution to the understanding of God is encapsulated in his formulation of the Ontological Argument. This argument is a philosophical approach that attempts to prove God's existence based on the very concept of God being the greatest conceivable being. Anselm posited that if we can conceive of a perfect being, then that being must exist in reality because existence is one of the attributes of perfection. In other words, if God exists only in our minds and not in reality, then we can conceive of a greater being that exists both in our minds and in reality. This leads to the conclusion that God, being the greatest conceivable being, must exist.

This concept has profound implications for theology, as it shifts the discussion of God's existence from empirical evidence to a purely logical and philosophical basis. Anselm’s work laid the groundwork for future philosophical theology discussions regarding God's nature and existence, influencing numerous theologians and philosophers thereafter.