With respect, your argument is that God created the universe, and causation is a feature of the material world.
So where there are only two possibilities, in this case a self-existent world or a created world, only one of the possibilities can be true, and the most reasonable explanation will be the acceptable one. Which, then, is the more likely or reasonable a world that we agree exists, in which cause and effect is a known phenomenon, or a supposed external source that is assumed to have those same features of our known world, upon which the theist must depend in order to argue for what is claimed? Both hypotheses can be denied without contradiction, and so neither of them is demonstrably true, but I contend that my argument is the more reasonable. For if the universe is necessary, then God is not. And while we cannot of course demonstrate that the universe is necessary, we know for certain that it exists, but in the case of God we have no such assurance.
Heat, precipitation, oxygen and nitrogen etc supply our needs for life; objects degrade and die and new objects appear from the old constituents and then grow to maturity, ensuring the continuity and the cyclical balance of life. So the undeniable fact is that the universe exists as a sustaining power. Why then is it necessary to look for a further sustaining power? And why should the physical world be created? That last point is known as the argument from sufficient reason. A self-existent world doesnt require an explanation or need a reason for being, but if a thing is created there must be a reason or a purpose for its creation. So
what is it?