Interesting question. I'm sure there are interesting answers in this thread, so I will tag this for later reading with the following:
One possible answer: If there was clear evidence that one god existed yet everything else in this world would stay the same. (Quite hard to do. Let's say that for example all humans would feel and hear her/him/it in their head all at once, once a year, like a global absolute delusion. This would leave clear and unequivocal evidence that god did exist.) It would be quite difficult to love god the way the world today is. Of course, if all would know that one god existed there would be very different problems in the word. One can try to imagine how people of different languages and cultures would still end up in religious war as everyone would know that there is one god and it's the same for all. I presume there would be fighting over who is the true representative of god on earth, unless of course, in my example, god would make it clear who that person is or isn't in its annual "speech in the head".
Perhaps this novelette (https://en.wikipedia.org/wiki/Hell_Is_the_Absence_of_God) is an interesting read on the subject as it appears to touch on it in a way (although I only read the very beginning of it, so not sure how much it's on this subject, but the premise seems to fit with this thread.)
