People like Robert Jeffress give “two-kingdom” theologians a bad name. (Get up to speed here).
Even if one embraces the idea that the Sermon on the Mount or the Great Commission should not dictate government policy, Christians are still required to speak and act when the government exerts itself in unjust, untruthful, and hateful ways.
My favorite two-kingdom thinker is retired University of Massachusetts political scientist Glenn Tinder. Here is what Tinder says in the “Social Transformation” chapter (4) of The Political Meaning of Christianity:
…if Christians are even more pessimistic about human beings than are conservatives how can they favor reform? How can they do anything but cling to all institutions, however unjust, that counteract the chaotic potentialities of human beings and achieve a degree of order? There are three interconnected answers to these questions.
First of all, Christian principles place one in a radical–that is, critical and adverse–relationship to established institutions. The Kingdom of God is a judgment on the existing society; the imminence of the Kingdom of God symbolizes its impermanence. Jesus was crucified because his presence and preaching were unsettling to reigning religious and political groups. Jesus did not seek the violent overthrow of these groups, but neihter did he show much concern for their stability…
The second answer to the foregoing questions is that these basic attitudes have to be acted on. This is a matter of spiritual integrity. To be opposed to the established order in principle, but in favor of keeping it exactly as it is, is an incongruity necessarily destructive of prophetic faith. Beliefs are not genuine unless they affect one’s conduct as well as one’s mind. To anticipate the coming of the Kingdom of God is merely sentimental, a private frivolity, unless one seeks ways of reshaping society according to the form of the imminent community. The Christian universe is not, as we have seen, an eternal and changeless order; it is a universe moving, under the impetus of the Word of God, toward radical re-creation…
Finally, however, it must be said that Christianity forbids us to assume the inevitability of failure. It requires hope, and hope pertains to the immediate, as well as the eschatological, future…It is reasonable to be skeptical concerning the possibilities of social transformation. But human beings have no warrant for holding fixed opinions in this matter, for they cannot know the kind or degree of change God intends to effect in history. And those who accept Christian principles do know, through Christ, that all things move toward the Kingdom of God, however humanly incomprehensible the movement may be…