Christianity was new. New ideas, new things, and new ways are often difficult to embrace. The old tried ways of centuries were easier and more comfortable. Hebrews is written to people who had embraced the new and were now struggling with staying with it to the finish. Some of the converts to Christianity were contemplating going back to Judaism. This epistle is God’s answer to that idea. Christianity is better. It is a better way. It is a better covenant. It is a better faith. 
The writer cites more than eighty references to the Old Testament to present his argument. This book is a commentary on the Old Testament. This epistle examines customs, and shows Jesus Christ brought better customs. The writer presents Jesus Christ as better. The author compares Jesus to Angels, Moses, priests, Aaron, Melchizedek, and Abraham. 
Who wrote Hebrews? There are several candidates and we are not positive which is correct. Those considered are Paul, Apollos, Barnabas, and several others. This has been discussed and debated now for two thousand years. The most common choice is Paul for a variety of reasons. Whoever wrote the book did not attach their name to the MSS. The most important issue in this invaluable book is not who wrote it, but the message it contains. 
Instead of the book beginning with the name Paul or Peter or James, this book begins with God. God owns this epistle, so ultimately the author is not relevant. There are 22 books of the New Testament after the gospels and Acts. There are nine books to churches, four books to individuals, then nine more epistles. Hebrews is the beginning of these nine books as Romans was to the first set of nine books. The former set of epistles addressed the moral law. These epistles address the ritual law. Both groups of nine end with prophecy. The first group ends with second Thessalonians and the coming of the Lord and end time events. This group that begins with Hebrews, ends with the book of Revelation.
The New Testament church was well aware that God instructed the building of the Tabernacle. God gave David the blueprints for the Temple. The conundrum for the early church was how can we discard that which was so aptly given by God himself? The book of Hebrews was written to solve this conundrum.
The Hebrew faith was codified in the Mosaic law and the Old Testament rituals. How should the New Testament church view these now? Christ was not a Levite. He was not of the lineage of Aaron. Weren’t people who died on a tree cursed? Should the church lay aside the feast days that had been a part of Jewish life for several millenniums? The decisions to be made needed divine direction.
Christianity brought a whole new way of life. The evolvement into New Testament ideology was facing some difficult decisions. For Christianity to blossom and flame into the world wide religion intended by God, these things must be resolved.  
This is why we have the book of Hebrews. God revealed his perfect completion of all Old Testament types and shadows. Hebrews is the majesty and ministry of Jesus Christ. Here God reveals his original intent and finished purpose in Jesus Christ the savior of the world.