That in God there is no matter
Matter is not a principle of activity because, as Aristotle tells us, efficient and material causes aren’t the same. God being the first efficient cause, he is not matter.
Those who hold that matter comes first acknowledge then that natural things must exist by chance. (See the primordial soup and the “chance” creation of amino acids, successively larger molecules, then simple microbes, all the way up to humans, all as a result of “chance” mutation and error selected for by the environment. What does “selected for” mean? It’s a metaphysical mess these materialists are in.) If this natural matter must exist by chance, creation would then exist by chance. (I’m not sure this is a great argument. I do know that if things DO NOT exist by chance, that cleans up and explains lots of philosophical problems, while chance runs contrary to reason and causes more problems than it explains.)
Matter cannot become a cause of a thing unless it is altered and changed. God being immovable, if he was matter, would be unaltered and unchanged, therefore would not have power to act.
The faith asserts that God created all things not out of his material, but out of nothing.
David of Dinant asserts that God is prime matter. (Prime matter is raw matter without form. It is the metaphysical raw material of the cosmos.) He says if God wasn’t prime matter he would differ form prime mater and they would not be metaphysically simple. (Simple means without part, or compound.)
He is wrong because for things to differ they must be similar other than the difference or differences. Two species differ, but are of the same genus, for example. Things that are diverse, however, are so by themselves. They are entirely distinguished from the other, and as such can be simple of themselves. God is pure act. Prime matter is pure potency. (Checkout Metaphysics book 10 here. Also, Scholastic Metaphysics by Edward Feser and of course Uncle Thomas in the big Summa. It’s worth it.)
That in God there is no composition
God being pure act, he cannot be composite. In all composite things there must exist potency and act. Components are made one by the presence of both act and potency. They are actually united because they were potentially united. God cannot be composite.
Not being composite, he has no components.
Composites are potentially disassemble-able. (H2O and electrolysis) If something is disassemble-able, it has the potential to not exist. God cannot have this potency because he necessarily exists. (He also contains no potency, being pure actuality as we have already seen.)
All composites require a compounder. We know God is the un-moved mover. There is none prior.
In metaphysical genus, the more simple a thing is the more perfect of an example it is. Fire is the perfection of hotness, as it contains no cold. So, whatever is most excellent (think telos) must be the simplest. God being the most excellent thing in existence mus also be the height of simplicity. (Do not confuse Thomist simplicity for modern notions of this. It’s not basic, dumbed-down, or whatever. It’s perfect elegance and fitness for the job. Think economy of all things and perfect, simple, fitness, with the fewest moving parts, for Godness.)
Additionally, in a composite thing the good of it does not belong in a single part, but to the whole. (The goodness of a man isn’t in his foot, it’s in his wholeness.) God, being good, if he was composite would be good as whole, but his parts wouldn’t be. This would make something appropriate to God not good in him. This cannot be.
All things are compounds. There must be a prime unity before all composite things, which is God.
My commentary is in parenthesis.
I am reading the Fr. Laurence Shapcote, OP translation. I have the opera Latin/English 2 volume set from the Aquinas Institute. You can buy it here. I think you can find it in less expensive out of copyright editions if you look for the Dominican Friars Translation on Bezos’ site, or for free at archive.org.
I’m reading about 35 chapters per month. It’ll take about two years. A few pages a day will get it done. Join me.