I don't know what to think about God. Sometimes I think he exists and he's just testing us. Sometimes I think he doesn't exist. But if he does then the reason you're still here is probably because he thinks you still have potential to do something worthwhile with your life, that your mission isn't yet complete and he wants to see you complete it. That's what I try taking from it sometimes. Obviously we're here so we must be worth something.
God sees every life as equal, and values each one as important as the other, but it is us and human beings who put different values on each other. You may not see yourself as being worth while or valuable and feel that God should just take you away from this world, but God certainly doesn't feel this. He doesn't want your life to be wasted, he wants you to see yourself as he sees you, as a person who deserves to live and has a place in this world just like any other.