In which our God saint defines his terms. Be careful to use the words in the sense he used them, at least while discussing him.
1 From what has been said, then, it is clear that to become like God is the ultimate end of all. Now, that which possesses the formal character of an end, in the proper sense, is the good. Therefore, things tend toward this objective, of becoming like God, inasmuch as He is good.
Notes Do not read “like God” as “a god”.
2 Creatures do not attain goodness in the same measure that it is in God, though each thing imitates divine goodness according to its measure. For, divine goodness is simple, entirely gathered together, as it were, into one being. Indeed, this divine existing being includes the entire fullness of perfection, as we proved in Book One .
As a result, since anything is perfect to the extent that it is good, this divine being is His perfect goodness. In fact, for God it is the same thing to be, to live, to be wise, to be blessed, and to be whatever else seems to belong to perfection and goodness; the whole divine goodness is, as it were, His divine existing being. Again, this divine being is the substance of the existing God. Now, this cannot obtain in the case of other things.
We have pointed out in Book Two  that no created substance is its own act of being. Hence, if anything is good by virtue of the fact that it exists, none of them is its own act of being; none of them is its own goodness. Rather, each of them is good by participation in goodness, just as it is being by participation in existing being itself.
3 Again, not all creatures are established on one level of goodness. For some of them, substance is their form and their act: this is so for the creature to whom, because of what it is essentially, it is appropriate to be, and to be good. For others, indeed, substance is composed of matter and form: to such a being it is appropriate to be, and to be good—but by virtue of some part of it, that is to say, by virtue of its form. Therefore, divine substance is its own goodness, but a simple substance participates goodness by virtue of what it is essentially, while composite substance does so by virtue of something that belongs to it as a part.
Notes The closer your acts accord with your true nature, body and spirit, the closer you approach the good.
4 In this third grade of substance, in turn, there is found a diversity in regard to being itself. For some of them that are composed of matter and form, the form fulfills the entire potentiality of the matter, so that there remains in their matter no potentiality for another form. And consequently, there is no potentiality in other matter for the form of this type of substance. Beings of this type are celestial bodies, which actuate their entire matter when they exist.
For other substances, the form does not exhaust the entire potentiality of their matter; consequently, there still remains a potentiality for another form, and in some other portion of matter there remains a potentiality for this sort of form, as is the case in the elements and in things composed of the elements. In fact, since privation is the negation in a substance of something which can be present in that substance, it is clear that the privation of a form is found combined with the type of form that does not exhaust the entire potentiality of matter. Indeed, privation cannot be associated with a substance whose form exhausts the entire potentiality of its matter; nor with one which is a form in its essence; still less with one whose essence is its very act of being.
Now, since it is obvious that change cannot take place where there is no potentiality to something else, for motion is the “act of that which exists potentially,” and since it is also clear that evil is the very privation of the good, it is plain that, in this lowest order of substances, the good is mutable and mixed with its contrary evil. This cannot occur in the higher orders of substances. Therefore, this substance which we have said is on the lowest level holds the lowest rank in goodness, just as it has the lowest grade in being.
Notes All follows even if there are not actual celestial bodies in which form fulfills the entire potentiality of the matter. Next Hamlet’s question: to be is a good.
5 Still, among the parts of this sort of substance composed of matter and form, an order of goodness is found. In fact, since matter, considered in itself, is potential being and form is its act, and since composite substance is actually existent through form, the form will be good in itself; while the composite substance is so in so far as it actually possesses form; and the matter is good inasmuch as it is in potentiality to form.
Besides, though anything is good in so far as it is a being, it is not, however, necessary for matter which is merely potential being to be good only in potency. For being is a term used absolutely, while good also includes a relation. In fact, a thing is not called good simply because it is an end, or because it has achieved the end; provided it be ordered to the end, it may be called good because of this relation.
So, matter cannot be called a being without qualification, because it is potential being, in which a relation to existing being is implied, but it can be called good, without qualification, precisely because of this relation. It is apparent in this conclusion that good is, in a way, of wider scope than being. For this reason, Dionysius says, in the fourth chapter of On the Divine Names: “the good extends to existent beings and also to non-existent ones.” For, this non-existent thing—namely matter understood as subject to privation—desires a good, that is, to be. It is, consequently, evident that it is also good, for nothing except a good thing desires the good.
6 There is still another way in which the goodness of a creature is defective in comparison with divine goodness. For, as we said, God in His very act of being holds the highest perfection of goodness. On the other hand, a created thing does not possess its perfection in unity, but in many items, for what is unified in the highest instance is found to be manifold in the lowest things. Consequently, God is said to be virtuous, wise, and operative with reference to the same thing, but creatures are so described with reference to a diversity of things.
And so, the more multiplicity the perfect goodness of any creature requires, the more removed is it from the first goodness. If it cannot attain perfect goodness, it will keep imperfect goodness in a few items. Hence it is that, though the first and highest good is altogether simple, and the substances that are nearer to it in goodness are likewise close to it in regard to simplicity, we find some among the lowest substances to be simpler than some of their superiors, as is the case with elements in relation to animals and men; yet these lower simple beings cannot achieve the perfection of knowledge and understanding which animals and men do attain.
7 So, it is evident from what has been said that, though God has His own perfect and complete goodness, in accord with His simple existing being, creatures do not attain the perfection of their goodness through their being alone, but through many things. Hence, although any one of them is good in so far as it exists, it cannot be called good, without qualification, if it lack any other things required for its goodness.
Thus, a man who is destitute of virtue and host to vices is indeed called good, relatively speaking; that is, to the extent that be is a being, and a man. However, in the absolute sense, he is not good, but evil. So, it is not the same thing for any creature to be and to be good without qualification, although each of them is good in so far as it exists. In God, however, to be and to be good are simply the same thing.
8 So, if each thing tends toward a likeness of divine goodness as its end, and if each thing becomes like the divine goodness in respect of all the things that belong to its proper goodness, then the goodness of the thing consists not only in its mere being, but in all the things needed for its perfection, as we have shown. It is obvious, then, that things are ordered to God as an end, not merely according to their substantial act of being, but also according to those items which are added as pertinent to perfection, and even according to the proper operation which also belongs to the thing’s perfection.