Probably nothing. Where I’m from, provincial government officials were sworn in on the power of the king, which was seen as shitty. Many people take there oath laughing at the stupidity of it, being sworn in on a power you don’t recognize and you would oppose for the next few years.

Only recently this « tradition » was totally abolished.

So my guess is that swearing on a holy book is only a show for « tradition » and it don’t mean much in this day and age.