What book of the bible says life is meaningless unless you fear and obey God?

Answer 1

Ecclesiastes:12:8-14

8: Vanity of vanities, saith the preacher; all is vanity.

9: And moreover, because the preacher was wise, he still taught the people knowledge; yea, he gave good heed, and sought out, and set in order many proverbs.

10: The preacher sought to find out acceptable words: and that which was written was upright, even words of truth.

11: The words of the wise are as goads, and as nails fastened by the masters of assemblies, which are given from one shepherd.

12: And further, by these, my son, be admonished: of making many books there is no end; and much study is a weariness of the flesh.

13: Let us hear the conclusion of the whole matter: Fear God, and keep his commandments: for this is the whole duty of man.

14: For God shall bring every work into judgment, with every secret thing, whether it be good, or whether it be evil.