Recently disendorsed NSW Liberal candidate, David Barker, expressed concern that Julia Gillard was "anti-God" and that a non-Liberal vote would be a vote for Muslims, thus reintroducing religion, kicking and screaming in protest, to the campaign agenda.

Associated with the NSW Christian right, Mr Barker's comments raise the question of whether Christians in Australia expect a Christian prime minister.

Before the 2007 Australian federal election, a Victorian Christian minister sent an email to his supporters, in which he claimed that God had told him to anoint Peter Costello as the future prime minister of Australia. John Howard would win the election, then hand over the leadership to Costello. He allegedly went to Parliament House to fulfil his God-given mission.

Apparently, it wasn't a God-given mission. Or, at the very least, divine and human wires got crossed. In my view, there could be a need to revisit this minister's expectations of how God might communicate with him, but that's for the theologians to sort out.

However, it highlights a significant problem with the way Christians relate to politics — they are way too 'Old Testament' about it. Anyone who is making a claim that God has told him to anoint the future leader is being very B.C. for a Christian minister.

In other words, it is a common Christian mistake when thinking about politics, society and the church to look at things through your Old Testament, rather than your New Testament, glasses.

Nowhere in the New Testament is there any concept that a Christian 'prophet' might be given word from God on who should govern the land. The arrival of Jesus changes all of that theocratic language, and the role of 'prophecy' changes: it becomes a call to recognise the authority of Jesus, and to follow his teachings and his call to turn back to God.

The New Testament famously calls on Christians to "be subject to the governing authorities" (in Romans 13:1) but it certainly does not say, "go and appoint the governing authorities yourself". In fact, it says quite the opposite. The very next verse suggests that if you resist an authority, you are in fact resisting God, because God is in control ultimately of who leads and who doesn't.

We sometimes hear Christians saying that only a Christian leader will do, because "righteousness exalts a nation", but that is an Old Testament idea (Proverbs 14:43, to be precise). That was a call to the ancient Jewish nation to obey God's commands so that the nations around them (who worshipped other gods) would see how the worshippers of 'the one true God' thrived, and perhaps realise he was the living deity, unlike their things of stone and wood.

Righteousness is no doubt a good thing (it's good to be good), and there is plenty to be learned from the Hebrew Bible in many areas of ethics, character and godliness, but Christian leaders ought to be more reflective in the way they use the various parts of the Bible to push their points. In short, they need to make sure they are being Christian about it.

Some Christian leaders (not many, it must be said) are claiming that Julia Gillard has no right to be Prime Minister because she is an atheist, and the majority of Australians are not. They are correct to note that Aussies still believe in God (67 per cent at least), but they are wrong to say that being an atheist disqualifies you — even in the eyes of Christians — from being prime minister. They may once again be invoking an Old Testament understanding of national leadership, not a New Testament one.

In fact, what they are doing is mistaking the offices of government with the positions of church leadership. It would indeed be appalling if the leaders of national church bodies were not themselves believers in God. It happens, and when it does it is horrifying. Worse than appointing a Collingwood coach as head of the Bombers. But that is the church we are talking about, not the nation.

For Christians, the difference between the two is of profound importance. The Christian church has plenty to say and do on behalf of the nation (I'm all for social involvement rather than separatism), but it was never part of the plan that we should run the place. Or it shouldn't be.

In the A.D. period — what Christians call the age of the church — the idea of 'God's nation' no longer exists. When it is invoked, it is always a mistake, be it Constantine's Europe, King James's England, or modern America. Or Australia. Christians care deeply about the nation, and in their finest moments do all they can to "seek the good of the city" (even if that is a quote from a book in the Old Testament!). But the gospel of Jesus transcends and transforms our understanding of the nation, breaking down barriers between people and (at least in its ideal form) modelling a different kind of 'nation'.

Australia isn't the most godless nation on earth, but nor are we God's nation on earth. In Christian understanding, that title doesn't belong to any nation, but only to the rag-tag collection of God-botherers, who gather together from many nations, many backgrounds and many political persuasions as what we call 'church'.

Dr Greg Clarke is Director of the Centre for Public Christianity.