I agree it is a great mystery. As a fervent reader of Nancy Drew and The Hardy Boys as I was growing up, I learned the first thing they did was search for clues. Could our first clue be God is Creator. Those who are creative are seldom satisfied with creating a single thing. They continue creating. I believe our second clue is that we are servants of God. Those who have servants, have work or a purpose for them. Third, Jesus mentioned there are many dwelling places, which I take to mean many ways to serve, many purposes.
Finally, on Earth we are given choices. If we are given a choice in heaven of where and how to serve, how much thought have we put into it?
I know many hold no belief in purgatory/purification before entering heaven. I do. If there is a place for me in heaven, and if a purpose is to reach out to those in purgatory, if it aligns with the will of God, that is where I would like to lend a hand.