"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 of a usurpation on one side or the other, or to a corrupting coalition or alliance between them, will be best guarded by an entire abstinence of the Government from interference in any way whatever, beyond the necessity of preserving public order, and protecting each sect against trespass on its legal rights by others."