re: The purpose of separation of church and state

James Madison was an integral part of the writing of the Bill of Rights. He grew up in Virginia which was heavily tied to the Church of England (Anglican Church in the colonies). Madison had a family friend who was a Baptist preacher who was jailed by the colony since he preached a church doctrine other than that of the Anglican Church. Madison, like other Virginians, paid taxes to the colony who used some of the tax revenue to SUPPORT Anglican churches and help pay Anglican preachers. No other denominations received such support.

Easily findable in any book on the writing of the Constitution or a biography of him.