The idea that God is uncaused is a Lynchpin of Theism. It is the basis for arguing God as the uncaused cause and unmoved mover of many philosophical argument for God, and is a view almost universally held in Theistic definitions of God.
Theist explanation of God’s being uncaused:
God exists because he is necessary (being necessary, in part, means being uncaused)
God’s is necessary because of his nature
Nature -> Necessity -> Existence
Now I know that to a lay-person (or even someone actually trained in philosophy) this may look like a chain of causation. And that's because it is, and one that can be undone quite easily.
The Following argument assumes three views on God and one view on metaphysics: 1) that God is a necessary being 2) God’s nature makes him necessary 3) God is outside of time (relevant to a hypothetical rebuttal) 4) self causation is impossible (because it is absurd)
P1. If God is not necessary, then he must either be contingent or not exist
P2. God is not contingent (this is because God is here defined as necessary)
SC 1: If God is not necessary, then he does not exist (This is the trichotomy of P1 reduced to a dichotomy by P2)
P1a. God’s nature is either self-caused, caused, or non-existent
P2a. God’s nature cannot be caused (Again, this is because God is here defined as necessary)
P3a. God’s nature cannot be self-caused (because self-causation is here regarded as impossible)
SC2: God’s nature does not exist (last option left in the trichotomy of P1a)
P1b. If god’s nature does not exist, then he his not necessary (necessity would be part of God’s nature the way having 4 sides is part of the nature of a square)
P2b. God’s nature does not exist (SC2)
SC3. God is not necessary
P1c. If God is not necessary, then he does not exist (SC1)
P2c. God is not necessary (SC3)
C: God does not exist.
This argument is a bit redundant, because SC2 is enough to show the conclusion provided we assume the premise P: all things which exist have a nature. But I wanted to be through.
For P1a, some might try to argue for a “not-caused and not self-caused” option. While that may be conceivable, the Theist explanation of God’s being uncaused I outlined above IS the explanation of a forth option for P1a. To say God’s nature is exempt from causation because God is necessary would be a circular argument. A second option would be to say that God’s nature is outside of time, and only things which being to exist need a cause. However, being outside of time is part of God’s nature. We have reached another circular argument. We could run the entire above argument again replacing necessary with eternal, and a few other relevant swaps and reach the same conclusion. A final option is to simply assert that God’s nature is exempt from all causality (without appeal to necessity or eternality). To do such is to abandon reason altogether and just start making shit up.
In short, there is no good way to argue that God is uncaused, and what sort of God is a caused God? No God. That's what sort of God.
People who argue that God is necessary because of his nature fail to realize the circularity of this position. “God is uncaused because he is a necessary being, and he is a necessary being because of his nature, and his nature exists because he is a necessary being”. No God, then no God’s nature. God’s nature must be caused or self-caused. If self-causation is impossible, then god’s nature is impossible, and therefor he does not exist. The alternative is circular argument or bare assertion.
S= Necessary. T=Contingent. ~E= Does not exist. N= Nature. L= Self-caused. C= Caused.
~S > (T ^ ~E)
C: ~S > ~E
~N > ~S
~S > ~E