Anthology of Related Fictional Works of Different Genres

Issue
Though assuming this board pertains primarily to the composition of short stories and novels, I would like to write a fictional book of narratives, epistles, speeches, poetry, etc, resembling the writing of the Bible, though not comprising a religion. I have not yet begun to form what character or plots I want to include in this book, as my mind is plagued continually with a fog, preventing me from even getting started.

Question
In light of these things, there are two questions which I would like to ask: one, how do I overcome this mental block, or exercise my brain so that I can think more clearly and invent the material I want to invent, and two, how do I go about creating the material for this book?

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Thank you.