I don't think there is ever a way to determine the reason for human existence. I'll back this up by saying this: the reason I don't believe there is a known purpose for the human race in particular; if there was, then that would mean that our universe would have a set end in mind. If the end of the universe was present in its beginning, then we would be in the mere deterministic unfolding set of initial conditions, the end would also be known, which in turn means that the universe would be a pointless exercise.
If you're at your destination, why make the journey? If you know the answer, why ask the question? That is why future is, and must be, profoundly hidden to any and all entities, whether they be a supernatural deity or a mere human. Otherwise, life would have no meaning. Life doesn't need to have a purpose; it's just a journey for us to take to reach the destination, or if you will, the end.