God's Volition

Does God have a Will?
Summa Theologiae I, Q19, a1, and SCG I.72
 
For Thomas, this pretty easy. Everything that has intellect also has will. Every substance is striving in some sense to perfect its own nature. If a substance is intellectual, then it moves towards its own perfection with understanding. But to move with understanding is precisely to move voluntarily, by the exercise of will. This will be especially true of God, since He understands Himself perfectly.
 
However, there is a problem: God is unmovable, immutable. So, He cannot be said to move toward His own perfection. He is essentially His own perfection. But when a substance rests in its own perfection, that perfection remains its natural end. And when an intellectual substance rests in its own perfection, that resting is resting with understanding, which is by definition the state of delight. So, God perpetually delights in His own perfection. But delight is a function of the will, so God has a will.
 
In the SCG, Thomas also points out (in paragraph 8), that God, as first agent, is supremely free. Nothing can move Him or make Him do anything. To act with free will is essential to being free, so God must have a will.
 
Does God will other things than Himself?
 
Summa Theologiae I, Q19, a2, and SCG I.75
 
So, God will His own perfection, and so He wills Himself. Does He also will other things? Given that God is essentially in a state of perfection, which is also a state of perfect happiness in which His will is at rest, is there any room for Him to will anything else? He has no needs or deficiencies to fill. He can’t be any happier than He would be if He willed nothing but Himself. No additional object of the will can add to His happiness, if ‘adding’ implies a kind of increase. (Objection 3)
 
In addition, if God willed more than His own essence, then His will would be divisible. Or, at the very least, His act of willing would be complex. But God is simple. (Objections 1 and 4)
 
Moreover, if He did will something else, it seems that the value of that other thing could be said to “move” His will by attraction. But God is immovable. (Objection 2)
 
In response, Thomas appeals to the self-dispersive nature of goodness. Good things (including especially good people) have a natural tendency to spread that goodness to others, even if doing so doesn’t add to their own happiness. To good to others is a sufficient reason in itself for acting. Since God is maximally good, this dispersive nature is especially true of Him.
 
Thomas makes the point in a slightly different way in SCG, paragraphs 3 and 4. We’ve established that God loves Himself. Whatever loves itself also loves to some degree the things that resemble. Every actual thing resembles God to some degree, so God naturally loves all actual things.
 
God wills Himself as the sole proper and immediate object of His will, but He wills other things insofar as their existence is a fitting effect of His perfect goodness. Just as He understands all possible things by understanding His own essence, so He wills all actual things by willing His own perfection. There is a single act of will in God, just as there is a single act of understanding. And these two acts are the same act.
 
In response to objection 2, Thomas argues that God is “moved” only by His own goodness, and so His immovability is not compromised.
God doesn’t will things in order to add to His happiness. He wills them simply because and insofar as it is good that they exist.
 
Thomas explains in SCG I.77 why God’s willing multiple objects is compatible with His absolute simplicity. God wills multiple things only insofar as they are included (“comprehended”) in His goodness, just as He knows multiple things by knowing Himself in His infinite power. In paragraph 5, Thomas argues that the multiplicity of objects of will is less of a threat to divine simplicity than multiple objects of understanding were, since the will acts for the sake of the goodness that is in the object, not for some value existing in itself. Hence, there is no obstacle to a simple will’s willing multiple objects