The book of Hebrews is different from the last several books of the New Testament because it wasn't written by Paul, or at least most scholars don't seem to think it was. The author is unknown, but whoever is writing the book of Hebrews is a person who is encouraging his Jewish fellow-Christians to stick to their faith and not get embroiled in all the many laws and customs of Judaism again.
The writer of Hebrews talks about Christ himself and about how important he obviously is to the Christian faith:
"God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets, Hath in these last days spoken unto us by his Son, whom he hath appointed heir of all things, by whom also he made the worlds; Who being the brightness of his glory, and the express image of his person, and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high." (1:1-3)
He's saying that in past times, God spoke to his chosen people the Jews through prophets; people like Samuel or Isaiah or Jeremiah, who would delivers his messages. But now God has changed his method of interacting with humankind and has actually sent his own divine son to the world. But although Jesus came to Earth as a human, he is still the powerful and glorious son of God.
Chapter 1 is about establishing how Christ is more powerful and more important than the angels, because if the Jews trust in the words of God sent by angels, shouldn't they be even more invested in accepting God's messages when they come from his own son? Chapter 3 discusses how Christ is on a higher level than Moses because though Moses was a beloved and faithful servant of God, he was simply human, while Jesus Christ has a divine nature. Chapter 5 discusses the Levitical priesthood of the Jews and mentions how Christ is a type pf sanctifying priest because he cleanses us from our sins permanently, as the priests used to do temporarily with burnt sacrifices.
The writer of Hebrews' real concern for his audience seems to be their lack of growth in the faith--at a time when they ought to figuratively be "grown up" Christians, they are still acting like babies and still needing the most basic guidance to get through their lives.
Chapter 11 is one of my favorite parts of the New Testament because it talks about faith and gives examples of what faith does for God's people and how it has helped them in the past, even through the most painful of circumstances. This is the chapter that begins with the verse, "Now faith is the substance of things hoped for, the evidence of things not seen," which seems to be one of those passages that's often quoted and commonly mistaken for Shakespeare. This is a passage I go back and read when I'm having trouble with my life as a Christian--having faith in Jesus Christ can be difficult at times, but the eternal rewards are great.