Just a quick intro to Hebrews. It's a unique document in the New Testament for a couple of reasons.
First, it was probably a sermon before it was a letter. That's why it starts the way that it does and doesn't really have greetings, etc., on either end like you see in most of the other New Testament letters.
Second, it uses a lot of comparisons to explain life with Christ. Christ is compared to angels, Moses, an OT high priest and the mysterious Melchizedek. His work on the cross is likened to entering the temple to make sacrifice for sin and, more generally, the whole OT sacrificial system. Because you see a lot of comparisons, you'll also see a lot of OT references to specific Scriptures and more general events.
It's a great little book showing how Christ is superior over everything, especially that which has come before in the people's relationship to God. Enjoy!