There answer is "There is no why."
I personally believe humans have everlasting life, but the only eternal life we have is God's life imparted to us. That is, I have a beginning, although I will have no end.
I have a few ideas about discussing the existence of "supernature" to naturalists, but it depends on why they are naturalists. As to whether or not there is a God, I think the most powerful visible testimony in these days is the modern State of Israel.
“God's life imparted to us,” is (to me) “God's Love imparted to us.”
I believe in God. If I stripped all human ideologies out of the equation, all I would have to do is look at the stars in the universe, and recognize that they did NOT come into being on their own. The universe is orderly, and the laws of physics demand that it be so.
Our universe, or galaxy, is only one of billions. God says the worlds were greater than the grains of sand on all the beaches of the world. I believe it. The photos we have access to concerning space tell us that we are not alone, and we are here because we have a purpose. We are lucky if we find that purpose in this life. But that doesn't mean we should waste the life in idle pursuits. There is so much to learn, and really, when push comes to shove, the only thing that "goes with us" into the Afterlife is our intelligence.