To these reasonings the answer is thus given: although God could have made the world unchangeable in act, and did not, he was not envious; for it belonged to his supreme goodness that he made the world, but to his wisdom that he allowed it to be changeable, so that through the changeable we might be changed into the unchangeable. For everything changeable implies that something is unchangeable; everything moving implies that something is at rest. Therefore I say "unchangeable in act," because he could not make anything unchangeable by nature; for every created thing, from the fact that it is created, has a beginning of its existence: by the same reasoning it has an end, in act or by nature, for every thing is bounded by two limits. Furthermore, it does not follow that if the cause is unchangeable, the effect is unchangeable. One kind of cause is efficient, another formal. The efficient cause is that which moves and works so that a thing may exist; as the craftsman is the efficient cause of his work, and moves it, and works so that it may exist; yet it does not follow that whatever is predicated of the craftsman is also true, or the contrary, of his work. For it happens that a work is long-lasting while its maker is not. Similarly, since God is the supreme craftsman of all things, and the efficient cause, he himself is unchangeable, yet the things created by him are not therefore unchangeable; indeed, it is impossible that things created by him should not be changeable, since whatever has a beginning naturally has an end.
Everything that is begotten tends toward destruction.
Concerning the formal cause, however, it is true that if it itself is unchangeable, the effect too is unchangeable, and conversely, as if whiteness is changeable, the white thing is also changeable. Thus, since humanity, which is the substantial nature of man and the formal cause, is changeable, its effect too is changeable, that is, the making of a man. Since, then, God is not a formal cause but an efficient one, although he himself is unchangeable, things are not therefore unchangeable.
And although many things in this world seem to happen by chance, nevertheless they do not happen apart from God's ordinance, who knows how and in what way each thing comes to be. For "there is no thing," as the philosopher says, "whose origin is not preceded by a legitimate cause and reason." Whence Christ says in the Gospel that not even one sparrow falls to the ground without God (Matth. 10).
To the next argument this answer is given: many things happen in sin, and by means of sin, and yet are not themselves sins, and are from God; as the knowledge which one acquires with an evil intention — namely with a view to human favor, or earthly gain — is possessed by means of sin, and yet is from God. Similarly, power which one acquires by simony is acquired in sin and through sin, and yet is from God. Similarly money which is acquired through usury is possessed in sin and through sin.
Likewise, although human flesh occasionally has its origin from sin, that which it is, is from God.