Some more thoughts on the relationship between the church and politics.
1. We are all political, whether or not we claim any 'involvement in politics' or have explicit ideas about government. Life is constantly lived in the light of power, implicit ideas of what is good for me and for others, and a relationship to governing authorities. We cannot actually be 'apolitical'.
2. We must recognize that politics can never be separated from worldview/worship. This was obvious in the ancient world, but is masked behind a veil of liberal secular neutrality in modern society. Politics always invokes 'gods', morality and a vision of the good life. There is no neutrality with regards to God and the kingdom. Whereas the world always seems to think spirituality is really about politics, we say that all politics is really about spirituality.
3. As Christians, then, we cannot avoid politics or political choices. The whole of life is under the rule of Christ and everything must be related to Him.
4. The political stance of the church is based upon the coming of the kingdom of God. This is all about the creation of a new world order. It is very political in the sense that the world will gain a new ruler (Jesus) and a new administration (kingdom) with completely new policies (law of Christ)! The vision of the new creation (Rev 21-22) is all about God bringing in a new political system of heaven ruling earth - the rule of Christ (Ps 2). The old corrupted world order will be overthrown (Rev 19).
5. The Church is, then the in-breaking of this future world order now - it's a foretaste of the reign of King Jesus. It's the new creation already at work in this world. In that case, the church is, de facto, heavily political in that it says that all power belongs to Jesus, that only his policies can work. We represent the politics of new creation and are governed by King Jesus. Note that a lot of the language describing the New Testament church and its internal processes is heavily political and drawn from the realm of government: assembly (=church), presbyters, citizens and city, nation/people, kings/kingdom. The weird thing about us is that our politics really belong to the re-created future world ("my kingdom is not of this world") and not to this world. This DOES NOT MEAN a privatized, individualized approach to following Christ. Our following of Christ has huge social and economic implications but the context of living this out is most properly the church (e.g. Acts 2 and the redistribution of wealth).
6. How then do we relate to the politics of this world?
Firstly, we still live in the old fallen creation even as we represent the new creation. We submit to its structures and ways (Rom 13), even as we know that they are passing away and ultimately irrelevant (to the extent they do not acknowledge Christ).
Secondly, we witness to the kingdom's way of doing things, but not on the world's terms. We live out our own politics (peace, a new view of power, love, justice etc) even as we submit to the structures of this world. We are the new paradigm of humanity and we are the destiny of the world. We are a public sign of what society and culture might be if they accepted the kingdom.
Thirdly, because they are irreparably fallen, idolatrous and corrupted by sin, the governing systems of this world largely rival Jesus, and their policies largely contradict the policies of the kingdom of God (state as Babylon in Revelation, generally negative view of the 'powers' in the NT). This does not mean that everything about them is bad, nor that they are as bad as they could be. From one perspective, they do good. As Romans 13 makes clear, they find themselves under God's sovereign rule and are used by Him for the good of His people (note the 2nd person is used in that passage). And, of course, many Christians find themselves in these systems trying to do good and live out their discipleship. The point here is that our hope is not really for Christian governing authorities in this world - rather it is for the coming of the kingdom of Jesus.
Fourthly, we are to serve as we can, to seek the good of all men and the justice/righteousness of God in all we do and to influence for good wherever we are - including in our corrupt political system. It may be bad, but we don't have to let it be as bad as it possibly can be (i.e. slavery). All the time, though our hope is for the coming of Jesus. We are aliens and pilgrims in the political order of this world.