The Preeminent Bible teacher R.C. Sproul - said that if he were thrown into prison and could only have one book of the bible with him it would be Hebrews. REASON - it is so rich, it covers the entire scope of the history of redemption as well as showing how Christ fulfills all of redemptive history.
Anytime we approach new study we typically spend the first sermon explaining WHO was the human author, WHERE was the author when he wrote the book, WHO was he writing to, WHAT were the circumstances that set the context for writing? But when we comes to Hebrews we cannot be certain about the answer to any of those questions.
We are forced to do some detective work and some educated guessing.