This thought came from a “What caused the Big Bang” type of discussion.
Something had to cause the Big Bang, unless the Big Bang always existed (which is not possible, as it would have always existed as a point of singularity unless acted upon by an outside force – so then the question would be where did that force come from, and you would end up in a impossible series of circular questioning).
So, when discussing the Big Bang – something caused it – it is not possible to have something come from nothing (ex nihilo nihil fit) [Out of nothing, nothing comes].
In order for something to come from nothing, it would have to create itself. And something would have to predate itself before it could create itself. That is, it would have to exist, before it existed. This is a logical impossibility.
Nothing has ever come from nothing – philosophically and logically speaking, if there was ever a point in existence where nothing existed, then nothing would still exist – and because we do exist, we know there was never a time when nothing existed (Thomas Aquinas makes this argument in his Quinque Viae).
In fact, not even God could create himself; therefore God must have always existed (which is a central claim to the Judeo-Christian doctrine).
Additionally, God would be changeless (RE: The same, yesterday, today and tomorrow) – another foundational claim to central Judeo-Christian teaching, and God would need nothing, He would be complete and whole in his personage, being able to exist eternally without input or output (another central claim to the Judeo-Christian doctrine).