There are at least three compelling reasons Christians must be involved in politics and government. First, as citizens of the nation-state, Christians have the same civic duties all citizens have: to serve on juries, to pay taxes, to vote, to support candidates they think are best qualified. They are commanded to pray for and respect governing authorities…
Second, as citizens of the Kingdom of God Chrisitans are to bring God’s standards of righteousness and justice to bear on the kingdoms of this world…As former Michigan state senator and college professor Stephen Mosnma says, Christian political involvement has the “potential to move the political system away from…the brokering of the self-interest of powerful persons and groups into a renewed concern for the public interest.”
Third, Christians have an obligation to bring transcendent moral values into the public debate. All law implicitly involves morality; the popular idea that “you can’t legislate morality” is a myth. Morality is legislated every day from the vantage point of one value system or another. The question is not whether we will legislate morality, but whose morality we will legislate.
–Chuck Colson in God and Government