With the explosion of the Singularity, all space time began. "Let there be light". So what caused the Singularity? What was before (despite the fact there really isn't a "before" where the beginning of time is concerned. We just don't have the language to say otherwise)
Before the Oscillating Universe theory was disproved, it was plausible to think in terms of "always". Now we cannot. The Universe had a definite beginning and we know it will have a cold, endlessness which never ends. Why? What are the external forces that are causal to the origin of our Universe? Why do most people get a sense there is something beyond physical reality? Most meaning about 98% of the human population throughout history.
I don't think it makes sense to take Moses' words too literally here.
He was just telling a story to 600 clans of Hebrews that he was leading out of Egypt.
As for his reason for making this story up, he probably wanted to impress upon them the need for them to obey laws and not murder each other at the drop of a hat.
Consider the necessity for the various commandments he gave them -- they were cursing, lying, cheating, stealing, adultering each other's wives, coveting each others goods, having sex with beasts, children, and same sex sex, etc. Egypt was a very corrupt place, like all civilizations.
"Let there be light" (per the KJV -- in Hebrew it actually says "YHY AOUR" -- be light!) does not explain where God himself/herself/themselves came from. So you cannot treat it as a literal beginning. Moses has not explained the beginning of God. Perhaps God did not want to tell us. Or perhaps Moses did not want us to know.