Well I took the plunge and finally read The Shack. To say it was a compelling story would be an exaggeration but it is an interesting story. However, I have some real concerns.

First let me list some of my concerns. If you think you will get an understanding of the Trinity by reading this book let me say that you will only get a false understanding of the Trinity. I made a number of notes as I read the book. First on page 99 Papa says (Papa is an African American woman who is suppose to represent God - I would like to comment on how the author in trying to avoid one stereo type jumps right into another) "When we three spoke ourself into human existence as the Son of God, we became fully human." This is certainly not Biblical. Jesus became man, not God the Father, not God the Holy Spirit. He then continues on page 100, "Jesus, as a human being, had no power within himself to heal anyone." When Jesus became human He was still God and the power of the living God was still in Him.
The real shocking part of the story comes on page 110 when Jesus says, "I am the best (not only) way any human can relate to papa or Saraya" and then on page 182 He adds when He is asked if all roads will lead to Him, "Not at all" but He leaves the implication open that there are other roads. Just a few lines earlier He messes with the the verbs jumping from past to present and back again.
On page 145 he talks about hierarchy being the result of sin but there is hierarchy in the God head, read your Bible, and among angels, in the church (God's design so I guess according to this book He sinned) and in the family. This is Biblical. It is not sin.
On page 202 he seems to indicate that the Ten Commandments are sinful but misses the point that they reveal the character and nature of God. He avoids wrath and condemnation and says that it is not part of God's plan but it is contrary to Biblical teaching. God does punish sin, the Bible says so. There are so many ways that as I read this book I could not make it consistent with Scripture.
I have heard a few comments by some people that are really bothersome. One person said that the reading of this book changed their prayer life, I guess now they pray to a Black African American woman. Another said that it took the Trinity and our understanding of God out of the box. The box has been part of orthodox Christian doctrine for two thousand years but we need to take Him out of the box and put Him into one that we will define by a novel. Give your head a shake. Others have said that they finally understand the Trinity - oh you do do you. Compare this to the Biblical teaching and you will see that it does anything but give you a proper understanding of the Trinity.
I also see that there is a breaking of the commandment that you are not to make any representation of God. The commandment is clear, God must define Himself. To define God as an old man or an African American woman is totally against the commandment.
Part way through this book I suddenly thought that I was reading the fictional version of Grace Walk without the Biblical basis for what it was saying.
Why has a book like this one become so popular? People are hungry for the spiritual but they are not willing to go to the source of truth. We have become Biblically illiterate and therefore we cannot see the errors in books like this. It is not that this book is almost right because to get doctrine almost right is to get doctrine wrong. I believe it is a challenge for the church to address the deeper issue that is here and that is why does a book like this get such a following.
There is a humourous part to this. While I was reading The Shack the person who lent me the book came by with another book for me, the title, Christ in the Tabernacle by A. B. Simpson.
My recommendation is not to read the book but if you do remember that it is a novel and not the Word of God. It is not even sound doctrine.