Don't get upset because you cannot provide a verse which you think thwarts the Trinity....I have yet to find a Unitarian who can...of which, pretty much tells me their confidence level in their world-view...yes?[/size]
Personally speaking I have more confidence in the lack of evidence for the Trinity in the Bible than just about any other topic. It's simply not there. The whole Bible, all its principles, are contrary to it. If I accepted the Trinity I would have to throw the Bible message away. It's hard to debate something that is so outside the realm of what the Bible teaches.
The use of quotations in Hebrews is pretty unique and it links in with the opening of the epistle which simply says "God... spoke..." There is nothing like "the apostle Paul to the ecclesia in Jerusalem" and we don't even know who wrote it. That's because Hebrews is basically saying "forget any human ideas here: God already said this in the Old Testament." I.e. this is nothing new - God already spoke about the superiority of the things to do with Christ over the elements of the old covenant. And so the epistle is a series of Old Testament quotations proving this point. In chapter 1, for instance, instead of saying "as the prophet Isaiah says" it says "he said", i.e. God said it (Hebrews 1:1).