I've become convinced that Hebrews ought not to be called 'The Epistle to the Hebrews' so much as 'The Sermon to the Hebrews.' And Richard Bauckham has recently shown me the pervasive and fundamental significance of Ps 110 for Hebrews.
Is it possible that Hebrews is a sermon 'on' (in the first century sense) Ps 110?
For instance Heb 1 shows the divinity of Christ, climaxing with Ps 110:1 ('The Lord said to my Lord . . .'), whereas the rest of Hebrews goes on to show Christ's humanity, qualifying him to be our high priest, largely drawing on Ps 110:4 ('You are a priest forever, after the order of Melchizedek').