Theists like to argue that everything that has a beginning has a cause.
So far so good.
They say the universe must have a beginning and the cause must be God.
Then they say that God doesn't have a beginning, He was always around, so we don't need a 'cause' for God.
But you could just as easily say that the universe has always been around. Yes, I know: the Big Bang, but the Big Bang caused the universe to be in its present state, it didn't 'begin' the universe.
Of course, when you discuss this area, it's pure theory (with a small t) and speculation. From the point of view of science, the Big Bang traces back to a singularity and the 'trail' goes cold at that point. From the point of view of religion, we've got a few vague chapters in a 2000 year-old book. Both the universe and God could have been farted out a monkey's butt for all we really know.