Of God and His Creatures2. The good of a part is ordained to the end of the good of the whole, as the imperfect to the perfect. But things become objects of the divine will according as they stand in the order of goodness. It follows that the good of the universe is the reason why God wills every good of any part of the universe.
3. Supposing that God wills anything, it follows of necessity that He wills the means requisite thereto. But what lays on others a necessity for doing a thing, is a reason for doing it. Therefore the accomplishment of a purpose, to which such and such means are requisite, is a reason to God for willing those means.
We may therefore proceed as follows. God wishes man to have reason, to the end that he may be man: He wishes man to be, to the end of the completion of the universe: He wishes the good of the universe to be, because it befits His own goodness.* The same proportion however is not observable in all three stages of this ratiocination. The divine goodness does not depend on the perfection of the universe, and receives no accession thereby. The perfection of the universe, though depending necessarily on the good of some particular components, which are essential parts of the universe, has no necessary dependence on others, although even from them some goodness or beauty accrues to the universe, such things serving solely for the fortification (munimentum) or embellishment of the rest. But any particular good depends absolutely on the elements that are requisite to it: and still even such goods have adjuncts that go merely to better their condition. Sometimes therefore the reason of the divine will involves mere becomingness, sometimes utility, sometimes also hypothetical necessity, but never absolute necessity, except when the object of God's volition is God Himself.
1.85 : That the Divine Will does not take away Contingency from things
1.87 : That nothing can be a Cause to the Divine Will