This may come as a relief to you: you can ignore all the complicated answers! In U.S. English, this one is easy as pie.
I was always, always, always taught this: the way to tell how to conjugate for a subject which sounds like it could be either singular or plural is to simply remove the prepositional phrase from the sentence. You would then conjugate based on the sentence without the phrase.
So in your example, if we remove the prepositional phrase "of society and the religious world," we're left with the sentence, "The whole [was/were] strongly impacted by this new religious view."
Now is it easier to tell which one is right?
It sure is to me. Any perspicacious ear can detect the correct choice is "The whole was strongly impacted by this new religious view." Because saying "the whole were strongly impacted" in American English just…sounds wrong. And that's because it is.
That's the helpful part of the trick: it allows one to rely on their ears for the answer. It's much easier to discern that "the whole" is a singular subject without the prepositional phrase there to obfuscate matters.
After all, it's not "the whole are greater than the sum of its parts," right? :-)
From now on, it should be a cinch to tell what the right choice is in this situation.
Isn't that a cool tip? For it, you can thank Mr. James Briggs, English-language scholar (and tenth-grade teacher) extraordinaire…