What is relevant here is whether religious faith is the essential part of the identity of Perrotet and Morrison. And, if it is, whether there is an impact on public policy. And, if so, whether the greater impact is on social and sexual issues, like abortion and euthanasia, or on economic policy issues, like government spending and the alleviation of poverty and inequality.

There has already been a shelf-full of articles and books about Morrison, many of them pointedly examining his Pentecostal faith. He is open about it, embraces its enthusiastic style of worship, and makes it central to his community and parliamentary networks. He even invited the media inside his church to see him worshipping. The identification has done him no harm.

Expect a similar avalanche about Perrotet; the new boy on the block is commonly described in code as a "conservative Catholic". As a Catholic myself, I know that "conservative Catholic" has many meanings, from ordinary social conservative to a member of a disciplined internal church movement.

In Perrotet's case, the use of the term means he is a member of or associated with Opus Dei, a recognised conservative group within the church. To the general public it is somewhat shadowy, and to most ordinary Catholics it is very private. It was vividly featured in Dan Brown's novel The Da Vinci Code. Perrotet attended Redfield College in Dural, where the school chaplains are from Opus Dei. The description also locates him as a member of the Right faction within Liberal Party internal politics.

The study of religion and politics is a growth area, stemming from fascination in a non-religious age from those who know little about it. For most of the 20th century there was interest only in the impact of denomination on voting.. We've come a long way in Australia since attention turned to the in-house Liberal Party faction, the pro-family Lyons Forum, during the Howard era.

One high point was the Kevin Rudd-Tony Abbott era of federal politics. These two religious combatants used each other's religious faith to signify what they were for and against - socialist versus conservative.

For Rudd, the Anglican with a Catholic background, it was Christian socialism, by which description he appealed to the religious centre to reinforce the traditional social justice connection between the Labor Party and Catholics, Methodists and other Christians. He wrote prolifically about it. He also notably took media conferences outside church in Canberra on Sundays.

Abbott, the former Catholic seminarian, determinedly tried to rubbish that view, projecting his own identity as an orthodox religious social conservative with strong ties to the Sydney Catholic hierarchy. It defined his time as health minister, and later prime minister, on issues like abortion and same-sex marriage. He advertised his connection to Cardinal George Pell.

Religious faith is an essential part of the personal identity of many political leaders. Authenticity is a valuable commodity in politics, and for some leaders their faith can strengthen that impression with some voters. However, at the same time, the religion "brand" is tarnished and even trashed in large parts of modern society.

Religious political leaders send various explicit and implicit signals to the community. Some are received positively. The adherents of their churches receive those signals as reassurance that government is in safe hands. The wider community of non-believers also include some who do not share religious attachments, but are not put off by them. They may even value them and be attracted to such leaders.

READ MORE:

However, for many in the community religious faith is a negative red light signalling that the political leader is opposed to modern secular values; or at least an amber light signalling "watch carefully" and "proceed with caution".

The Christian community should see the ascendance of Morrison and Perrotet, from the same party in the same state, as a sign that, far from being frozen out, Christians - even non-mainstream Christians - continue to rise to the top to play central roles in public life. While increasingly concentrated on one side of politics, they rise up in surprisingly large numbers given the overall characteristics of modern Australian society.

In the past 15 years there have been three overtly religious prime ministers: Rudd, Abbott and Morrison. One of Perrotet's recent predecessors in NSW was Mike Baird, also a public Christian.

The lingering question remains: does it make any difference? Is religious belief an incidental aspect of the character of political leaders, secondary to party affiliation, political philosophy and/or personal style? Or is it a driving force which can be clearly detected in their policies?

Despite many studies of Morrison, concentrating on his adherence to an individualistic reading of a so-called prosperity gospel that suits his political inclinations, the answer to this question remains a grey area. This will not prevent similar studies which will see Perrotet through the same lens.

It is a decent question to ask. Just don't expect any answers which clarify modern politics.