My personal favourite is Ecclesiastes which, apart from a couple of lines of slop added by a later author, has little to do with Abrahamic religion and is more just a little nugget of proto-existentialism.
“Meaningless! Meaningless!”
says the Teacher.
“Utterly meaningless!
Everything is meaningless.”
What do people gain from all their labors
at which they toil under the sun?
Generations come and generations go,
but the earth remains forever.
https://www.biblegateway.com/passage/?search=ecclesiastes%20...