Those states which have an official state religion are not democratic in nature.

Mostly they are either outright theocracies, like Iran, Saudi Arabia and several other countries in the Middle East, or very authoritarian in nature like Egypt and Jordan.

The Christian church has an especially awful history in Europe, having spawned numerous wars and many atrocities, notably the systemic and systematic persecution of the Jews, which reached its apotheosis in the Holocaust (which Jews call the Shoah) perpetrated by the Nazis.

In more recent times, the intolerance and violence of various Islamic fascist groups has caused enormous suffering and harm.

Religion is, of its very nature, irrational, illogical, mystical and, very frequently, violently intolerant of dissent.

These are qualities that have been a disastrous influence across history and certainly have no place in the governance of any country.

As others have pointed out, the Christian faith is riven with sectarianism and theological and philosophical disputation.

This is very much the case for all of the monotheistic religions (which believe there is only one god), although non-theistic religions like Hinduism and Buddhism also are prone to it as well.

Christian influence is waning across much of the developed world due to various reasons, notably the impact of higher education and an associated realisation that science is infinitely more successful in explaining the world than is religion.

Mainstream Christianity is most affected by this decline, while the more extreme and radical evangelical and Episcopalian movements are still growing. 

PNG's ancient religious beliefs were animistic in nature while Christianity is a colonial imposition. 

I cannot imagine a worse idea than deciding to embed a foreign religion in the PNG constitution.

It will be a licence for the religious to interfere in the political system and history shows us that this invariably leads to bad outcomes.

PNG's founders got it right in the first instance and James Marape and his colleagues should leave well enough alone.