The role and seriousness of religion in society has ebbed and flowed a lot historically. There is reason to believe that during much of the Hellenistic period

The role and seriousness of religion in society has ebbed and flowed a lot historically. There is reason to believe that during much of the Hellenistic period and before/after, most ancient Greeks saw the Gods as more of a folk tradition, for example. Hence the rise in schools of philosophical thought independent of religion. Likely many other Pagan societies had such ebbs and flows. Ancient China went through similar periods IIUC. It’s also hard for me to believe that Renaissance era Italians were really fervent believers given all the corruption involved in the Church (placing rich people as Popes, tons of Popes and priests having affairs and using the church money to live lavishly). Which is likely what led to the Reformation and the wars of religion - basically a return back to taking religion very seriously. Historically it also seems to vary a lot based on class, with the upper end of society (by class or education) tending to be less religious. For example during the 19th century the average person was still quite religious in much of Europe, but the most educated classes had already become secular and begun to openly express Atheism. Then you look at things like the Wars of Religion following the reformation - most likely, this provided an excellent backdrop to motivate your soldiers with a real cause for fighting, which rulers used to accomplish their more practical goals of expanding their realm.