Our business, as Christians, is the establishment of the kingdom. It is a kingdom that takes its beginnings here in this real world, and aims at the fulfilling of this world, of bringing this world to its destiny. But it is not a kingdom that can be identified with the Roman Empire any more than it can be identified with a capitalist paradise or a Marxist utopia. The dimensions of this kingdom reach to domains that politics can never reach, to the realms of the "kingdom that is not of this world." It is that extra dimension that Christians are called on to participate in making a reality. Politics, as well as everything else that is human and earthy, has its place in the establishment of the kingdom. But the political reality is not the ultimate value, nor is it the sole instrument for the bringing of the kingdom.
To accept any system as gospel is to accept the limits of that system, to refuse to see further than that system or to see more clearly or to see sooner or to render judgement on it or to prophesy against it. It is merely to ratify the limits such a system places on the kingdom. It is to turn our faith into a religion. And it makes little difference whether it is a religion of the right or of the left. Every time we have taken the gospel in to the political game in this way, we have ended up betraying the gospel.
Vincent Donovan, in Rediscovering Christianity, pages 165/6