I tend to agree with Voltaire when he said “if God did not exist, it would be necessary to invent him”. Now, I’m Christian myself, but I do believe that, even if he didn’t exist, humanity generally has a need to believe and he serves a purpose. However, simply imagining that he exists doesn’t work, one has to actually believe in his existence for it to be meaningful.
To use your Santa Claus example, I’m sure there are some adults that are inspired by him, but they’re no more inspired by him than any other ubiquitous and altruistic character. Santa Claus has a different affect on children because they legitimately believe he exists and how he inspires them is independent of his existence. Children wouldn’t be any more or less inspired by him because they receive the same stimulus (ie, gifts for good behavior) now as they would if he actually did exist.
However, I also think that Santa Claus is not a completely apt analogy. It works fine when comparing prayer and the placebo affect, for instance, but there are some things that are directly affected by the existence or non-existence of God, particularly for those who believe in an interventionist deity. So if you’re judging based upon similar criteria to Santa Claus, then no he doesn’t need to be any more real for people to be inspired by his love, or whatever other properties they believe he has.
This depends. If you believe in an interventionist God, then it is important that he exists because things will be different in some situations whether he exists or not. If, however, you believe in a non-interventionist God, then it doesn’t matter. Since my beliefs are closer to the latter, I can say that it really isn’t that important whether he actually exists or not because even if he doesn’t exist, as long as I believe that what I believe is how the world is, then my behavior will be unaffected regardless of whether he exists or not until and unless I run into a situation that my beliefs are directly contradicted by the cirumstances.
I would say no. If I freely and openly believed that God did not exist, I wouldn’t believe what I believe. To return to your Santa Claus example, he wouldn’t inspire children anymore because they now know that there is no correlation between their behavior and gifts. Of course, it’s really just the parents, but if they find that out, Santa Claus is now an imaginary altruistic person, and the parents are just rewarding/punishing their children for their behavior.
And what’s the point of worshipping something that we know doesn’t exist? Would anyone go to Church/Temple/etc. and worship a god that they knew didn’t exist? It seems like an exercise in futility, doesn’t it?
Inside of my beliefs, no. But, obviously, those with interventionist beliefs may say differently. Religion inspires people because they believe he exists; he’s an example pure love, forgiveness, and all sorts of traits that we hold dear. He can still serve the purpose of inspiring people to those ends and others whether or not he exists. However, as also demonstrated by atheism, that doesn’t mean that his non-existence means a lack of those values either, but it does mean that the inspiration for those can be found in other ways. If the idea of God exists to inspire those traits, and people know he doesn’t exist and can get that inspiration elsewhere, then he doesn’t serve a purpose
So, to make a short answer to your general question, as a religious person myself, I would say it doesn’t really matter whether he exists or not, as far as inspiring moral virtues, justice, the arts, etc. as long as people believe that he does. However, the fact that he doesn’t need to exist to inspire those doesn’t actually say anything about whether he exists one way or another, doesn’t say anything about what purposes he may serve that we can’t observe (eg, origin of the universe), and is just a critique on the needs of man.