Dr. D.G. Hart has posted a good article interacting with critics of two kingdom theology. While I disagree with Dr. Hart on the the extent to which the Scriptures speak to matters of civil ethics, nevertheless I agree with him entirely on the principle of the Spirituality of the Church.
The Scriptures teach that the magistrate is required to uphold the whole of the Moral Law as it applies to the civil sphere, and the church must proclaim this truth as it is found in Scripture. But the church is not a political action committee! It would be a shame to the name of Christ and an overthrow of jurisdiction for His Church to behave as though she were a political entity.
It is a common error amongst erstwhile Reformed evangelicals to think that the Church has a duty to do whatever any individual Christian may do. Christians as citizens in the civil sphere ought to be involved in politics to whatever extent they are able, and to shape their politics in keeping with the Scriptural standard of civil ethics. But it would be an abuse of the authority Christ has left in His church for her officers to convene Synods and Councils as though she were a political party calling a convention.