This is a very good question.
In the 5th edition rules, there are 2 pages on religion and ethics which I think also appeared in the 4th edition. In this section, the GM makes some very interesting points which seem to have been ignored by many players. I won’t quote it all, but extract the main points …
Religion & Ethics
Most people were on the face of it very wary of getting involved in Wars of Religion following the 30 Years War which devastated much of Germany. This wariness did not prevent conflict and religion still played a vital role in how people made decisions. Indeed, there is barely a letter written by an officer or ruler which has survived to the present day which does not in passing mention Providence, the Almighty, or God in some respect.
Taking diplomatic and even military action to protect oppressed minorities of your faith in other rulers’ lands was a common act. Charles XII of Sweden threatened to fight the Hapsburg Austrians to free the Protestants of Silesia from Catholic domination. (Various other conflicts are also mentioned.)
On the positive side, the prominence of religion gave men of the time a different outlook on the acts of men. High standards were expected in all but the most bitter conflicts. Officers would be permitted to go home on parole, and would not fight until released to do so by their parole being lifted by agreement. They could even stay with their unit in the field, but avoided doing any duties so as to conform with the terms of parole! Why? Due to a code of honour, and because the Divine Presence would know if you did wrong. Those who did, no doubt repented at length as old age approached. Whole armies could be granted Honours of War to avoid bloodshed, the word of the general being good enough to secure this. When the Duke of Marlborough had numerous villages in Bavaria torched to get the Electoral Prince of that land to march and give battle, the Duke was loudly condemned at home and elsewhere. In France mothers warned their children that ‘Marlbrouk’ would come and get them if they don’t behave. Minorities could be protected from persecution by the interests of their powerful co-religionists in other States. The Protestants in France were an obvious exception, but several attempts had been made to help them in earlier decades. France proved too powerful to have her will bent towards tolerance by diplomatic means. After all the Galician Church considered Protestants condemned to Eternal Damnation, so forcibly converting their children was in their eyes a saving grace, preventing them going the way of their parents after death.
There was no deliberate and massive genocide as seen in the 20th century at the hands of atheist regimes, thankfully, so perhaps despite the strife it was to some extent an Age of Reason. Where butchery took place it was usually the result of an event such as storming a town, when men – having seen many of their friends killed in assaulting the defences – would go on an orgy of destruction. Still, this was well known and the Honours of War system tried to provide a solution to prevent such inevitable brutality.
You should take into account religion when playing the game, as praise from a religious arch enemy can be damning indeed, perhaps even costing you Honour!
I think these extracts from the rules demonstrate that there is a link between religion and honour, that people of the time had a strong sense of honour which was founded on their religious belief. This does not sit easily with some players who have no sense of religion in their own lives and who live by a value system based on utility or pragmatism. If you repudiate the notion of God or organised religion, adopting the view that you are free to chose your own values and codes of behaviour, then whether you like it or not you are rejecting the historical norms of 1700 and putting yourself at a disadvantage when trying to understand how these people made decisions and how they were expected to behave.
A player who tries to play historically and respect the philosophies and religion of 1700 would expect to be criticised if he broke his word, to lose support and be frowned upon by his nobles. He would lose moral authority. To behave dishonourably would at best be seen as cheating, tarnishing the honour of those who follow you. Far better to play fair and accept the judgement of Providence even if this means you lose, for no man can fight the will of God.
Of course this doesn’t mean that player’s can’t be sneaky and fight hard to win, but it does require players to maintain credibility with their own supporters and with other players. If players, or groups of players, continually change sides, break treaties, fail to honour promises, then they will be seen as untrustworthy which ultimately will make it far harder for them to achieve support for their own plans from those nations they have wronged.
A high honour score does not in itself signify that you are playing with honour, but it is impossible to maintain a high honour score if you are determined to play dishonourably. Sooner or later the temporary factors which supported your honour score will diminish in their effect. Equally a low honour score can occur for many reasons, but it would be highly unusual for such a score to remain low if you play within the moral norms of 1700 and respect the role of religion in daily life.
The praise of co-religionists may help honour and so the Pope does have a great deal of influence. Perhaps someone who has played the Pope in a game is more able to demonstrate how easy or difficult it is to wield that influence. I’m not sure whether other religions have a Head who can also be a separate player, so it is hard to comment.