Facts are such a pain in a debate... ;)
The civil Government, though bereft of everything like an associated hierarchy, possesses the requisite stability, and performs its functions with complete success, whilst the number, the industry, and the morality of the priesthood, and the devotion of the people, have been manifestly increased by the total separation of the church from the State (Letter to Robert Walsh, Mar. 2, 1819).
Strongly guarded as is the separation between religion and & Gov't in the Constitution of the United States the danger of encroachment by Ecclesiastical Bodies, may be illustrated by precedents already furnished in their short history (Detached Memoranda, circa 1820).
Every new and successful example, therefore, of a perfect separation between the ecclesiastical and civil matters, is of importance; and I have no doubt that every new example will succeed, as every past one has done, in showing that religion and Government will both exist in greater purity the less they are mixed together (Letter to Edward Livingston, July 10, 1822).
I must admit moreover that it may not be easy, in every possible case, to trace the line of separation between the rights of religion and the civil authority with such distinctness as to avoid collisions and doubts on unessential points. The tendency to a usurpation on one side or the other or to a corrupting coalition or alliance between them will be best guarded against by entire abstinence of the government from interference in any way whatever, beyond the necessity of preserving public order and protecting each sect against trespasses on its legal rights by others. (Letter Rev. Jasper Adams, Spring 1832).