in the sense of the overall 'why does humanity exist?' my general belief is to breed and continue the species as we are animals and that is our primary function, survival, everything else we've made is a result of us standing upright and thus giving our hands free reign along with new-found boredom, "idle hands" were a plaything of nature long before the devil existed...
as for me individually, what is my purpose? i've no idea, though i've made it a point in my existence, as i figured out all the uniformity of human thinking long ago to 'make everything fit'... my self-appointed goal/purpose is to learn/know all that i can and make it all 'fit', all stories are applicable, all knowledge is made up, everything is true and at the same time a lie, like i said we human's primary function is that of animals and just to breed and survive as a species, thus all we've created, all we've 'learned' and 'discovered' is effectively all made up in our minds because we were 'bored' and wanted something to do with our new-found 'hands'... thusly i see no reason to discredit or throw away any of these ideas based on anything else... in my strange little world i've already got down how the gods and god get along, as well as all manner of fairy tales and mythos... its all true because 'why not?' science is basically magic, just because i know 'how' the trick is done doesn't make it any less amazing, therefore i see no reason to discredit either, both require the 'faith' in believing it exists to begin with...
strip away all the major details and all stories are the same... knowing that doesn't degrade anything, it just means those 'details' are that much more important and in the end we, all of us, are all the same and there is no real reason for any of this hate/violence of one another because really we're all just hurting ourselves...
the only sad part is this 'philosophy' doesn't really help in any sense towards this thing we crated called 'society', it really clashes with my purpose in life, but oh well, que sera sera...