from Scot McKnight:
Kingdom of God, instead of aligning with already existing political powers, created a new kind of kingdom with a new king, a new rule and redemption, a new people, a new law and a new sense of place. The ethic of the kingdom is for those people living under that king not for the public sector living under other kings.
It violates the integrity of kingdom theology to impose that ethic or vision on others and turns kingdom theology into a secularized (I mean that term as "worldly" not as in "secular humanism") alternative. One can't enter into kingdom ethics apart from living under the king and participating in that king’s redemptive rule. One compromises that kingdom and that rule and that king when one softens or adjusts it all to fit under another empire’s orders and ways of being.
The biggest mistake made in the Christian and politics discussion is to assume that what God has said to the covenant community (e.g., Israel, the church) is also for the non-covenanted people. To be sure, God’s will is God's will and therefore God's will for all, but the kingdom vision of Jesus is for kingdom people not for non-kingdom people. We are not called to impose kingdom ethics on the world but to call people into the kingdom.
The entire post can be read here.