Angels and demons are secondary causes, too.
1 We should attend to the fact that two things are required for providence: the ordering and the execution of the order. The first of these is accomplished by the cognitive power; as a consequence, those who have more perfect knowledge are called orderers of the others. “For it is the function of the wise man to order.” But the second is done by the operative power.
Now, the situations in these two functions are contrary to each other. For, the more perfect an ordering is, the more does it descend to small details; but the execution of small details is appropriate to a lower power, proportionate to such an effect. Now, in God the highest perfection in regard to both functions is found; in fact, there is in Him the most perfect wisdom for ordering and the most perfect power for operating. So, He Himself through His wisdom must arrange the orders for all things, even the least; on the other hand, He may execute the small details by means of other lower powers, through which He Himself works, as does a universal and higher power through a lower and particular power. It is appropriate, then, that there be inferior agents as executors of divine providence.
2 Again, we showed above that divine operation does not exclude the operations of secondary causes. But the resultants of the operations of secondary causes are within the scope of divine providence, since God orders all singulars by Himself, as we showed. Therefore, secondary causes are the executors of divine providence.
3 Besides, the stronger the power of an agent is, the farther does its operation extend to more remote effects. For instance, the bigger a fire is, the farther away are the things it heats. But this does not occur in the case of an agent that acts without a medium, for whatever it acts on is adjacent to it. Therefore, since the power of divine providence is the greatest, it must extend its operation to its most distant effects through some intermediaries.
4 Moreover, it belongs to the dignity of a ruler to have many ministers and a variety of executors of his rule, for, the more subjects he has, on different levels, the higher and greater is his dominion shown to be. But no ruler’s dignity is comparable to the dignity of the divine rule. So, it is appropriate that the execution of divine providence be carried out by diverse levels of agents.
Notes Every manager knows this.
5 Furthermore, the propriety of its order manifests the perfection of providence, since order is the proper effect of providence. Now, it is pertinent to the propriety of order that nothing be left in disorder. So, the perfection of divine providence requires that the excess of certain things over others lit reduced to a suitable order. Now, this is done when one makes available some good for those that have less, from the abundance of those that have more. So, since the perfection of the universe requires that certain things participate in divine goodness more abundantly than others, as we showed above, the perfection of divine providence demands that the execution of the divine rule be accomplished by those that participate more fully in divine goodness.
6 Besides, the order of causes is more noble than the order of effects, just as a cause is better than an effect. So, the perfection of providence is better manifested by the first order. But, if there were no intermediary causes carrying out divine providence, there would not be an order of causes in reality but only an order of effects, Therefore, the perfection of divine providence demands that there be intermediary causes as executors of it.
7 Hence it is said in the Psalm (102:21): “Bless the Lord, all His hosts; you ministers of His who do His will”; and elsewhere: “Fire, hail, snow, stormy winds, which fulfill His word” (Ps. 148:8).