Is the book of Hebrews an epistle or a sermon? The fact that it is an epistle is clear in the final 8 verses which contain the elements often found in New Testament epistles. In verse 22, the author describes his discourse as a "word of exhortation" (logou tes parakleseos). The Greek word for exhortation includes the broad ideas of warning and reproof as well as encouragement and comfort. It refers to a discourse prepared for oral delivery – a sermon. The author wants to convey the impression that he is present with his audience in the assembly as his words are publicly read. He specifically urges his readers to "bear with" his message. Perhaps he realizes that much of what he wrote contained strong rebuke. Of course, this is not something he regrets, as he hopes his words would become the means that God would use to encourage repentance and faith; however, he does seem to understand that hard words require patience and endurance to receive.
We can learn quite a bit about the composition of a sermon by looking at Hebrews as an example. We have seen how it provides strong encouragement and assurance for the rest and hope that lie ahead for the Christian, based on the sure promises of God. At the same time, Hebrews exhorts believers to endure discipline and resist sin lest they drift away from the faith. Both the encouragement and comfort based on what God has done in Christ, and the strong warning of judgment, serve the same goal – to save those who hear. The perseverance and preservation of the saints requires encouragement as well as reproof, and if we neglect one, we fail to preach the whole counsel of God which is designed to preserve us unto eternal life.