I’ve been posts various sermons recently and so am particularly interested in Dr Witherington’s posting on The Rhetorical Character of Hebrews:
This document [Hebrews], like 1 John is a homily , in fact D.J. Harrington has called it “arguably the greatest Christian sermon ever written down” It does not partake of the qualities of a letter except at the very end of the document (Heb. 13.22-25), and these epistolary features are added because this sermon had to be sent to the audience rather than delivered orally to them by the author. In fact, H. Thyen, after studying all the evidence for early Jewish homilies, has argued that Hebrews is the only completely preserved Jewish homily of the period, but this is overlooking 1 John, and James as well.
The article is “the text (but not the notes) of my Society of Biblical Literature lecture to be given next Sunday in Boston.”