All I can say is that the bible assertions are not nonsense. They are self consistent. They require an “implementation domain” that transcends our mortal coil, but cannot be shown wrong by any kind of reductio ad absurdam.
And the main question is not even “what?” but “who?” The “what” is there because of the “who.” Existence doesn’t just exist for the sake of existing. It’s got a purpose.
I’m not calling the Bible nonsense - I’m giving my interpretation of it. No one has to agree with me, obviously. As for a reason for existence, I see the answer to that question simply as God. God IS existence, and our reason for existing is to seek God.
Maybe that’s too simplistic, but it works for me.