A complete and total separation of church and state is necessary to protect both institutions.
Most people seem to recognize the need for a complete wall between church and state, but some people seem to disagree. They are mistaken; a strict separation between the institutions is necessary, or else both will be destroyed.
First, no free state cannot survive co-mingling with religion. An absolute necessity of a free nation is the ability to criticize and oppose your government. But how do you oppose God? A state that can claim religious authority raises itself beyond criticism, because a challenge to the state becomes a challenge to Supreme Law. And a state beyond criticism will inevitably become tyrannical, arbitrary and capricious.
Neither can religion survive the accumulation of political power. Churches are fundamentally composed of fallible mortals. Any church that gains political power will begin to attract men who seek power, and politically ambitious people by nature are skilled at climbing the ladders of authority. Over time, people of faith will be beaten out by the politically ambitious, and the church simply becomes another political party — the exact situation that governed the Europe our founders escaped.
The mixing of church and state destroys both. It cannot be allowed to happen.
Article from /r/Libertarian: For a Free Society