The author of the book of Hebrews, as well as the identity of the original readers, is unknown. The title “The Epistle to the Hebrews” implies that they were Jewish Christians.
This book is addressed to a local gathering of believers who discovered the reality of persecution over which they exercised no control. It addresses in a pastoral way the sagging faith of older and tired individuals who were in danger of relinquishing their Christian commitment. It seeks to strengthen them so that they may stand firm in their faith. It warns them of the judgment of God they would incur if they were to waver in their commitment.
No doubt the believers were subject to pressure to renounce their faith. And were vulnerable to doubts about Christ and to thinking about turning back to their familiar rituals and old way of thinking. As they thought back to the past, their Jewish tradition and ceremonies must have seemed wondrously attractive. Primitive Christianity had no parallel ritual trappings and no replacement or the temple. Christians met in homes, with no large central meeting place and no altar, priests, or sacrifices.
As we think back to our old ways of life, the “glory days,” our memories are oftentimes selective…we remember only the best of times. The pull of the old lifestyle can be strong.
Purpose — The writer urged the original readers to persevere in their faith, rather than turning from Christianity and returning to Judaism.
Theme — The comprehensive theme of the Epistle to the Hebrews is that of the absolute supremacy of Christ—a supremacy which allows no challenge, whether from human or angelic beings.
Central message — We will only realize our full eternal reward as believers if we appreciate the greatness of Jesus Christ and continue to trust God, rather than turning away from Him.
He addressed his readers consistently as believers. He wrote to encourage Christians to persevere faithfully, so that they will receive all that God wants to give them at the judgment seat of Christ. Our rewards are at issue in this letter, not our salvation. The writer did not want us to suffer loss, but to enter into our full inheritance, our full rest, the fullness of our salvation.
We live in a present-oriented culture that values immediate self-gratification. Many Christians are abandoning the faith because they do not appreciate the reward that they will receive, if they remain faithful to the Lord. This life is preparation for the next. We need to realize that God will judge Christians who apostatize. They will not lose their salvation, but they will lose much that they will wish they had never given up, if they stop walking by faith (Romans 8:18). It is hard to finish well, but it is possible (Jude 24; Hebrews 12:1-3). Our motivation should include a combination of the fear of God and the love of God, like the two wings on an airplane.
 Dr. Thomas L. Constable, Notes on Hebrews, 2017 Edition (published by http://planobiblechapel.org/soniclight/)