For quite some time there’s been contention and disagreement about who actually wrote the Book of Hebrews. When I was young, I was taught Paul wrote it. Nowadays, many say it wasn’t Paul, but perhaps Peter, or some other writer. Others say parts were written by different authors, almost as if to say the Book of Hebrews is a collection of writings assembled by a ghost writer.
I believe the book of Hebrews is a collaborative work by Paul, Luke, Timothy, and Mark. Let me explain why:
First, a good portion of it reads like Paul’s writings. For one thing, Paul, in his other writings will sometimes make a general statement, then back up to make corrections on the fly rather than "crossing it out" or starting the scroll over. The writer or writers of the Book of Hebrews do this as well.
Paul speaks with authority without hedge, as "Rabboni" rather than "Rabbi." Peter doesn't do this. Peter tends to make statements as a pastor, counselor, or even a student. Peter reaches out metaphorically, and even directly in appeals, to others for concurrence.
It should be noted Paul received special training from the Lord after his conversion as indicated in 2 Corinthians 12:1-6; 1 Corinthians 15:7-9; 1 Corinthians 9:1; and Galatians 1:15-17. He likely had insight no one else had.
Paul, though he was made the "Apostle to the Gentiles" by Jesus, as he describes in Acts 26:15-18; Romans 11:12; Acts 9:15; Galatians 2:8, still had a heart for his people, the Hebrews.
Paul writes in 2 Timothy 4:11-13
“Only Luke is with me. Get Mark and bring him with you, because he is helpful to me in my ministry. I sent Tychicus to Ephesus. When you come, bring the cloak that I left with Carpus at Troas, and my scrolls, especially the parchments.”
Paul’s getting on in years. He’s in a Roman prison, accompanied by Luke. Paul’s reflecting on his own people. He sends for Timothy to bring Mark, and his scrolls and parchments—his reference materials. Paul has a plan.
Paul is preparing to make a final instructional letter for his own people referencing his scrolls and parchments with the collaboration of Luke, Timothy, and Mark. When Timothy and Mark arrive with the scrolls and parchment, the four are equipped to write this final work of Paul's ministry. This collaboration is why no specific author is stated. I suspect they didn’t want to bias the audience of the Hebrews right at the start.
While my conclusion might be speculative, the evidence is not. Paul not only described, but initiated and orchestrated this situation in which such a potentially collaborative meeting would take place. I believe, together, the four of them wrote this work of edification and encouragement to the Hebrews.