Ah, this to me is the truly interesting religious question. While it is unclear to me why anyone would look to religion for the how, given what a good job science does and what a poor job all historical and current religions have done, it is equally unclear to me why anyone would think that the answer to why can be found in science.
For me the big why is the same as ones relationship with God, it is a personal and internal thing and should never be assumed to be an objective truth but a subjective one. Of course this is easy for me because I try hard to limit my reliance on belief in objective truth even for questions that lend themselves to experimental testing.
Unlike nihilistic, I do see value in asking some questions which I believe do not have objective answers, in seeking certain types of unverifiable knowledge. Specifically knowledge of self.
Just as one can look inside and find a moral code (you conscience), I think one can look inside and find answers to the big why. Of course this isnt as easy as sitting down and doing it, you must work at it. You know right from wrong, and you also know why. The more you work at it the clearer the answer becomes.
For me it has become clear that the why is all about interactions with humans. At first I thought it was simply one on one type interactions, and really all about love. While I still think that love is the most important thing, I have come to believe that there are various levels of human interaction that are all important: one on one, small groups (immediate family size, say 3-7), medium groups (tribe size, say 25-250), and large groups (represented by all of humanity, but also encompassing nations, religions, and even political groups).
I am here to contribute at all these levels. To love and be loved, to try and improve the human condition.
Of course this is an answer to why am I here, but not to the bigger question of why is the universe here at all, and why does it take the form it does (I think I once mentioned my theory on hydrogen and stars to you FL2). I have pondered that for much of my life, it is the question that took me from atheist to agnostic over a number of years.
I dont know why, I assume I will never know why in my current form.
But I have also been able to separate that question (to which there might be an objective answer), from the question of why I am here (which I am happy to answer in subjective terms).
Perfection says that why is a human invention, and I agree. As such it demands a human answer; why does have meaning to humans.
