What is the theme in Mick Harte Was Here by Barbara Park?

After death is a central theme in the book. One of the things that worries Phoebe the most about her brother's death is her feeling that she has no physical place she can point to that Mick is. One of the ideas that she discusses with her friend Zoe is her need to be able to visualize where Mick is. She has trouble seeing Mick in heaven because the descriptions of heaven that she has received do not seem to be any place that Mick would like to be. Zoe finally comes up with the idea that Mick is everywhere. Her reasoning is that if Mick is with God, and God is everywhere, Mick must be everywhere also. This is an explanation that Phoebe can accept.