My personal belief is that we are here to do the one thing that is difficult for God to do. That is to grow a soul, whatever a soul truly is.
Here is my reasoning. According to Genesis, God made everything in five days, with the exception of Mankind. I don't believe that those are literally five rotations of the Earth, but five of God's "work days". On the sixth day, He only did one thing; make Man in His image. That does not mean two arms, two legs, one head, etc. It means He made us like Him; spiritually. In essence, he gave the animal man a soul. That transformed man into Man. Then He rested. That implies that giving Man a soul was as hard as making the rest of the universe. Why did He do this? He, like the rest of us, wanted to grow. In order to grow, He needed to add to His current soul.
Through the trials and tribulations of living, our soul grows. As we fight and remain strong and faithful, regardless of how harsh our life becomes, our soul grows. As we help our fellow man overcome their problems, even as our own problems pull us down, our soul grows. That is why God isn't Santa Claus; giving us anything we want, or even need. You don't grow without some sort of adversity. If you can get through life without becoming bitter and resentful, they your soul is good and strong. When you die, the only thing left of YOU is your soul and that soul will join with God and make Him a little greater than He was. You have fulfilled your purpose.