There has existed from eternity someone unchangeable and independent being.
Cosmological argument consists in that everything must have a cause.
But then we have a problem -
of infinite regress (circular logic).
The argument begins with the premise that everything has a cause, but this is then contradicted by the claim that God does not have a cause. If we must posit a God as the cause of the universe, then it seems we must also posit a second God as the cause of the first, and a third God as the cause of the second and so on ad infinitum. So we shall have to accept that there are an infinite number of Gods. Either that or we must stop with a cause that itself has no independent cause. But if we must stop somewhere, why not stop with the Big Bang itself? What reason is there to introduce even one God? Of course, some might be willing to accept an infinite chain of Gods. But such a chain still wouldn't remove the mystery with which we began. For then the question would arise: Why is there such an infinite chain of Gods, rather than no chain?
Either there has always existed one unchangeable and independent Being, from which all other beings that are or ever were in the universe, have received their original; or else there has been an infinite succession of changeable and dependent beings, produced one from another in an endless progression, without any original cause at all.
The whole series of beings can have no cause from without, of its existence, because in it are supposed to be included all things that are or ever were in the universe, and this plan can have no reason within itself, of its existence; because no one being in this infinite succession is supposed to be self-existent or necessary (which is the only ground of reason of existence of anything, that can be imagined within the thing itself, as will presently more fully appear).
So there is a Prime Mover - uncaused cause.
The question why God has no cause is unanswerable.