Because modern scholarship is doing the same thing.
My interest in the theological and ideological roots of the American Constitution stem from a college paper a decade ago. I wrote a short ten-page thesis on Christianity and the formation of the Constitution...only to change my thesis half-way through my research: it was not just generic Christianity that substantially influenced America, but Calvinism.
In the last two years (with no college schedule to drive my time), I have had more opportunity to discover more non-Christian scholarly work on this subject. Now, I can write five times as much on this topic using secular sources alone.
Well, enough about me; here is a review of a relevant book I would gladly like for Christmas...it's only 98$ :-)
What is fascinating about the review is the critique: the lack of contemporaneousness of the book. It's about twenty years old (it took a while to get the essays published). Yet, from a non-post-modern viewpoint this is not a problem at all: if truth has historical manifestations amongst large aggregates of mankind (think nations), then the truth of Calvinism and Covenantalism for the continual maintenance of this American Republic is quite contemporary.
Can't get more relevant than finding the roots of our freedoms and returning to them! Of course, if mere "covenant" is recaptured without the Covenant of Grace in the hearts of Americans, then we are simply back (and are already there in many ways) to the Covenant of Works.
My prayer, especially for contemporary American Christianity is that she would return to her Calvinistic-Covenantal roots.
And that first begins with acknowledging the truths of history.