Objection 1. It would seem that corporeal creatures were not made on account of God's goodness. For it is said (Wisdom 1:14) that God "created all things that they might be." Therefore all things were created for their own being's sake, and not on account of God's goodness.
Objection 2. Further, good has the nature of an end; therefore the greater good in things is the end of the lesser good. But spiritual creatures are related to corporeal creatures, as the greater good to the lesser. Corporeal creatures, therefore, are created for the sake of spiritual creatures, and not on account of God's goodness.
Objection 3. Further, justice does not give unequal things except to the unequal. Now God is just: therefore inequality not created by God must precede all inequality created by Him. But an inequality not created by God can only arise from free-will, and consequently all inequality results from the different movements of free-will. Now, corporeal creatures are unequal to spiritual creatures. Therefore the former were made on account of movements of free-will, and not on account of God's goodness.
On the contrary, It is said (Proverbs 16:4): "The Lord hath made all things for Himself."
I answer that, Origen laid down [Peri Archon ii.] that corporeal creatures were not made according to God's original purpose, but in punishment of the sin of spiritual creatures. For he maintained that God in the beginning made spiritual creatures only, and all of equal nature; but that of these by the use of free-will some turned to God, and, according to the measure of their conversion, were given an higher or a lower rank, retaining their simplicity; while others turned from God, and became bound to different kinds of bodies according to the degree of their turning away. But this position is erroneous. In the first place, because it is contrary to Scripture, which, after narrating the production of each kind of corporeal creatures, subjoins, "God saw that it was good" (Genesis 1), as if to say that everything was brought into being for the reason that it was good for it to be. But according to Origen's opinion, the corporeal creature was made, not because it was good that it should be, but that the evil in another might be punished.
Secondly, because it would follow that the arrangement, which now exists, of the corporeal world would arise from mere chance. For it the sun's body was made what it is, that it might serve for a punishment suitable to some sin of a spiritual creature, it would follow, if other spiritual creatures had sinned in the same way as the one to punish whom the sun had been created, that many suns would exist in the world; and so of other things. But such a consequence is altogether inadmissible. Hence we must set aside this theory as false, and consider that the entire universe is constituted by all creatures, as a whole consists of its parts.
Now if we wish to assign an end to any whole, and to the parts of that whole, we shall find, first, that each and every part exists for the sake of its proper act, as the eye for the act of seeing; secondly, that less honorable parts exist for the more honorable, as the senses for the intellect, the lungs for the heart; and, thirdly, that all parts are for the perfection of the whole, as the matter for the form, since the parts are, as it were, the matter of the whole. Furthermore, the whole man is on account of an extrinsic end, that end being the fruition of God. So, therefore, in the parts of the universe also every creature exists for its own proper act and perfection, and the less noble for the nobler, as those creatures that are less noble than man exist for the sake of man, whilst each and every creature exists for the perfection of the entire universe. Furthermore, the entire universe, with all its parts, is ordained towards God as its end, inasmuch as it imitates, as it were, and shows forth the Divine goodness, to the glory of God. Reasonable creatures, however, have in some special and higher manner God as their end, since they can attain to Him by their own operations, by knowing and loving Him. Thus it is plain that the Divine goodness is the end of all corporeal things.
Reply to Objection 1. In the very fact of any creature possessing being, it represents the Divine being and Its goodness. And, therefore, that God created all things, that they might have being, does not exclude that He created them for His own goodness.
Reply to Objection 2. The proximate end does not exclude the ultimate end. Therefore that corporeal creatures were, in a manner, made for the sake of the spiritual, does not prevent their being made on account of God's goodness.
Reply to Objection 3. Equality of justice has its place in retribution, since equal rewards or punishments are due to equal merit or demerit. But this does not apply to things as at first instituted. For just as an architect, without injustice, places stones of the same kind in different parts of a building, not on account of any antecedent difference in the stones, but with a view to securing that perfection of the entire building, which could not be obtained except by the different positions of the stones; even so, God from the beginning, to secure perfection in the universe, has set therein creatures of various and unequal natures, according to His wisdom, and without injustice, since no diversity of merit is presupposed.
Source: Summa Theologica (New Advent)