This letter was written in 70 AD to the Jews who believed in Christ. They were the second generation believers and were being persecuted by the Jews and Romans.
The writer of this letter emphasizes that both Judaism and Christianity are from God but Christianity is more complete and perfect. He proves this by comparing Christ with angels, Moses and the high priest system of the Old Testament to show that Christianity has a better covenant and Christ is the perfect sacrifice. Salvation can only come from having faith in him.
He used the example of many historical figures in Jewish history to explain how to live by faith and encouraged believers to keep their faith despite persecution. Believers should encourage each other and look forward to the return of Christ.