The eighteenth and early nineteenth century political sermons of New England preachers are windows on the world of church-state relations in early America, and ones which only a few scholars of religious liberty have taken the time to look through. They are particularly valuable, in my view, for what they suggest about the manner in which founding-era Americans understood the meaning of establishment and disestablishment, and of the connections between religion and government.
Many of these sermons are collected in the two-volume set, The Political Sermons of the American Founding Era, published by the excellent Liberty Fund in 1991 and edited by Ellis Sandoz (LSU). They can be downloaded and enjoyed for free from the Liberty Fund site. — MOD