I agree with Donovan: The Word of God is superb reading material, many great lessons and the only true understanding of why we are here. I have read devotionals that have helped and I would say that a book called "Lessons of a sheepdog." (Phillip Keller.) very good lessons for anyone, especially the unsaved.

I find great comfort in reading God's holy Word.

I often find comfort in the Word of God (the Bible).

"Let your conversation be without covetousness; and be content with such things as ye have: for he hath said, I will never leave thee, nor forsake thee. So that we may boldly say, The Lord is my helper, and I will not fear what man shall do unto me."  Hebrews 13:5,6

Psalms and Proverbs can be helpful, even for the atheist or agnostic.