I understood that parts of the Bible talked about the vault of heaven and that the sky was a hardened dome. But, I never really understood the entire picture. I figured that people thought the sky was water because it was blue. It turns out that within Semitic cosmology that's just the color of the bottom of heaven of the firmament which is held up by the mountains. But, I never understood why the dome was spread-out like hard metal or resting on firm foundations, or the other bits that relate to cosmology. And it has a lot to do with how the world was created in the myth and what existed before and the picture people had of the universe.
Genesis starts out with basically a preamble, in the beginning, the gods created the heavens and the Earth. And then describes how they came to be. What's interesting is how the second line of the creation myth is just glossed over, and largely ignored. The first line we get, the third line is understandable, but what the hell is that second line saying?
1:2 And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
Sure, formless earth, nothing there, darkness are all understandable. But, what is the "face of the deep"? And the spirit of God moved upon the face of the waters? What waters? When did waters get created? If you read through the genesis account, water is never created. There's a lot of sections about dividing the waters by making the firmament and keeping it apart from the waters of the Earth. And allowing land to be exist, and gathering waters into seas, but never actually making the water. The reason for this is that at the core of the cosmology it isn't a creation ex nilho.
The universe was created out of a cosmic ocean. The firmament and the Earth divide the waters because its all waters. And cosmic ocean underlay all the cosmologies of the Semitic regions. The universe according to the Bible wasn't made out of nothing, it was made out of a formless ocean that was divided up. The reason for professing repeatedly in the Bible as to how strong and secure the firmament, how it's made of strong metal, and upon solid foundations and expertly crafted, is because it was a very real fear that the ocean might crush you. That Noah's Flood might very well happen and the waters will flow out of the vault of heaven and out from under the Earth, and our precarious little bubble might not exist.
7:11 In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.
8:2 The fountains also of the deep and the windows of heaven were stopped, and the rain from heaven was restrained;
And given the myth of the flood it was absolutely vital to assure people that such a thing would never ever happen again, with God's regrets, and pinky-promises and rainbows.
9:11 And I will establish my covenant with you, neither shall all flesh be cut off any more by the waters of a flood; neither shall there any more be a flood to destroy the earth.
9:12 And God said, This is the token of the covenant which I make between me and you and every living creature that is with you, for perpetual generations:
9:13 I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth.
It was a very real worry that the cosmic ocean would kill everybody., and much of the Bible goes to dissuade our fears of this. And in fact, because the sky is hard and metal and protects us, it's clear evidence for God.
Psalms 19:1 The heavens declare the glory of God; and the firmament sheweth his handywork.
And really, understanding this is rather devastating to Biblical cosmology and a lot of apologetics. There's a lot of stuff with like the Kalam Cosmological Argument that largely says that the universe was created ex nilho and science can't explain this, but God fully explains how this happened. But, the Bible never actually said that, it starts out with a cosmic ocean and a sky made of hard material on solid foundations, which attest to the handiwork of God. Far be it for Christianity to explain the Big Bang with a divine fallacy, they need to explain rather where that original cosmic ocean came from. The gods created the heavens and the Earth to divide up the waters, but that's doesn't explain the origins of the cosmic ocean.
The Bible doesn't actually fit that paradigm at all, it not even trying to answer to the question of what caused the initial expansion/existence of spacetime. It's answering very specifically how did the strong firmament of heaven and dry land get formed out of a cosmic ocean. The answer is "God did it", in fact God spent a solid 1/6th of the time he spent making stuff to make that firmament, that majestic roof fretted with golden fire (as Shakespeare put it). Spending the entire second day on it. Dry land was part of the third day. Then in day four God spends a lot of time adding bling to the firmament. Putting stars in it, and really big balls of light to travel across the firmament. The little tiny spots of light (which according to Revelations will fall to the ground during the end times) and the giant greater and lesser lights of the sun and moon, just to deck it out and give us signs for seasons and such. A lot of the OT is depended on this view of the universe, and really by coming to understand that, you really see how hollow various claims about how God explains the universe actually are. If you read the Bible, the authors have no clue what the universe is really like and spend a considerable amount of time explaining how why the cosmic ocean doesn't kill us, how the sky is hard as metal, and how awesome God is for making said firmament.
So the general theist argument that atheists can't explain the origins of the universe but God does, is even hollower, not just because the answers we have are really good and anything is better than the always wrong answer theists try to shove into every gap, but because the Christian God explains the origins of the metal dome protecting us from the cosmic ocean..