No one can say for sure where the person that we call I goes when the body stops functioning. For the atheist, the I and the body are the same, so the I goes nowhere, it's just ceases to exist. But, why does any thing exist at all. Why is there a universe, an earth, life, and why am I aware of it?
The material realist, those who believe that only matter is real, would say I'm aware of these things because I have a brain. But, who or what is the I that is aware? The brain is basically a super computer, but what good is a computer if there is nothing or no thing that observes the results of the computers computations. If we were just bodies acting out the computations of the brain, what makes me have different likes, or tastes in food, music, art, sports, and colors, and why do I have different political and social ideas than members of my own family. It is this difference from others, this me, that is not you, which makes me aware of myself as an individual; an I, different from your individual I.
God is the Perfect or Ideal I. In order for this Perfect I to be aware of Itself, God created other, like I's, which were imperfect, in order for the Perfect I to know it's perfection. We are those imperfect I's.