How did Anselm's first proof in Monologion move from good things to God?

In his Monologion, Anselm’s first proof of the existence of God is rooted in Neoplatonic thought. He begins by observing the existence of a multiplicity of good things in the world.12

Anselm argues that because these various things are all considered "good," they must all share or participate, to varying degrees, in one and the same absolute Good. He concludes that this singular, supreme Good—which is good in and of itself—is God. By moving from the observation of relative, finite goods to the necessity of an ultimate, objective standard, Anselm identifies God as the absolute and integrating source of all perfection.123