Isaac Backus quotes:

God has appointed two kinds of government in the world, which are distinct in their nature, and ought never to be confounded together; one of which is called civil, the other ecclesiastical government.

Now who can hear Christ declare, that his kingdom is, not of this world, and yet believe that this blending of church and state together can be pleasing to him?

When church and state are separate, the effects are happy, and they do not at all interfere with each other: but where they have been confounded together, no tongue nor pen can fully describe the mischiefs that have ensued.