The book sounds like an unholy tool of the Enemy after reading both the wikipedia plot summary and the Albert Mohler article. Simply put, the bible does not support the theology of "the Shack" at all, and the bible teaches in a number of instances against such theology.
To the point of this thread, the New Testament contains so many passages calling people to escape the coming wrath of God by trusting in the Lord Jesus by faith and living a sinless life deserving of our calling, that I see no real point in a debate except to research the bible and quote scriptures that show such.
I think I'll stop there as this debate could open many cans of worms I don't want to open such as the debate over a biblical understanding of the Trinity, mankind's inferiority and submission to God Who looks past this enough to save us through His Son so that we can be friends and children, whether God would ever give a revelatory mountain-top experience to a man or woman wavering in faith, and the problem of evil.
I would like to spiel a bit on the problem of evil as I believe it more than anything else is the driving force behind the novel and its message and perhaps why it has such impact on people. I myself see no other angle to understand why this novel captures so many minds beyond the clear contrived problem of evil plot and that someone actually has a God that the world so clearly loves speak forth at all, which the bible explains kills this as being a godly work immediately (I was going to quote some bible verses but this website does so much better:
http://biblereasons.com/reasons-why-the-world-hates-christians/).
I'll ponder more on the problem of evil though and get back to you guys and gals.