While I’m not exactly sure what you mean by “determined,” I would say the following:
God is Good (goodness itself). Man can know with his intellect that God is Good and that God is the ultimate good for man since God is the final cause for which man was made. Man cannot establish for himself that God is the ultimate good, he can merely recognize that this is a fact in objective reality. Why? Simply because God is, and man is utterly contingent on God.
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