I’ve said it many times before and I’ll say it again: I like imagine that Paul is the unnamed author of Hebrews. One of the major arguments I see rejecting this proposal is that Hebrews is so different from Paul’s other writings, both in style and content. But then I think to myself, “so what?” I’m not convinced that there were two or three Isaiahs or that there was a Jahwist, Elohimist, Deuteronomist, and Priestly source for the Pentateuch based on differences in style and content, so why should I be convinced that Paul couldn’t have written Hebrews. How do we know that Hebrews isn’t what a Pauline homily addressed to Jewish Christians would look like? Wouldn’t some differences be expected? Also, why this idea that someone has to maintain a single or general style of writing? I don’t know, the more I think about it the less reason I see to believe that Paul didn’t write Hebrews. Since we don’t know for sure who the author is anyway, I say that Paul is as good a guess as anyone else (especially given that a lot of the fathers of the Church attributed the writing to him).
Paul: Not the Author of Hebrews (Eric Sowell)
Is Paul the Author of Hebrews? (Brian Small)
NB that this topic was “was one of the sub-points of [Sowell's] Master’s thesis” and Small is a “Ph.D. candidate in New Testament at Baylor University [whose] dissertation is on the Book of Hebrews.” All this means is that they’re smarter than me, but alas, they’re both wrong!