The writer of Hebrews is unknown. The authorship has been a controversy since the earliest times. There is some evidence the apostle Paul was the author (Hebrews 13:23; 2 Peter 3:15), but it is inconclusive.
The audience for Hebrews is…Jews. If Paul is the author, then this is the only book he wrote when he did not have Gentiles in mind. While the book is not written “to” Gentiles, it has many things “for” Gentiles. Namely, that Jesus Christ is better than Judaism, angels, Moses, Joshua, Aaron.
Its Jewishness should cause us to be cautious when trying to apply it to the Church.