Frank, I think the point is that the document itself was declaring our independence from the monarchy and therefore we would no longer be "subjects" but "citizens" of a new government despite the fact that the final form of that actual government would not be completed until the Constitution was ratified.

It demonstrates that Jefferson had to even change his mindset seeing this was the first declaration of its kind against the British throne.

Overall it's just a neat fact that allows historians to get all excited. And they deserve to get excited once in a while. :)