Good, having the nature of both perfection and end, is expressed by creatures in two ways. First, as we said before, the creature has a certain perfection in lieu of its form, which is the proper end of generation. Second, the creature obtains perfection by virtue of its activity. Both of these goods can only imitate the divine goodness in a limited and imperfect way. As the end of generation, form is the goodness of creatures, but substances which are composed, metaphysically speaking, do not possess this end essentially. Substances composed of matter and form or essence and existence cannot contain their own form or existence by virtue of their being. They receive such goods from something external to them.
What we have, then, is an hierarchical order in which composite substances must receive their goodness from something which is essentially good. God, being his own essence, existence, and goodness, has goodness essentially. His goodness is not the end of some generation or the completion of some incomplete activity. All goodness in creatures is therefore a participation in His goodness. In the same way, God's essential being demonstrates that he is the cause of being in all things, His essential goodness demonstrates that he is the ultimate end of all creatures.