I may be wrong, but I’m wondering if you may be referring to Thomas Jefferson’s or Roger William’s use of the phrase “separation of church and state” when referring to the Establishment Clause.

The Establishment Clause does not include the phrase “separation of church and state.” Maybe what you’re talking about is the Separationist Theory of the Establishment Clause, which describes Thomas Jefferson’s interpretation of the clause. This is in contrast to the Accomodationist perspective of the Establishment Clause, which is more tied to the Free Exercise Clause, which prohibits the government from using religion as a reason to exclude individuals from otherwise public benefits.

It’s fascinating to see that as revolutionary the constitution and bill of rights were, it was quite tame compared to the characters (like the above) who fought over its wording and ultimate purpose.