I am absolutely sure that it is not to procreate, reproduce, live or die. Those things are part of the natural world and nature doesn't have reasons.
Your question requires God by the very definition of the word, "reason". Reason is intelligence and a design or plan.
People constantly ask about purpose of life, point of life, meaning of life, reason for existence, etc. It is reasonable that if God exists, that He put our need for purpose into our human nature to urge us to seek Him.