God!
I'm on a mission this year to read as much as I can about thought life and faith. I've picked up a lot of books and/or authors I've never heard of, like this one. It's on topic, though, so I wanted to read it.
Overall, there are a lot of great things in this book--I took plenty of notes and underlined a lot of passages. His emphasis on renewing your mind is spot on and supported in Scripture over and over again, as are his reference to the importance of spirit and truth.
However, I would encourage people to read carefully and prayerfully about what transforming your mind looks like. Yes, it absolutely changes our hearts and minds and conforms us to Christ; I hesitate to agree that it also means people will all have the same natural outcomes. Some of the most faithful, strongest Christians I know have health issues; it's not because they don't believe enough. Blanket statements about how our faith will manifest naturally (with wealth, health, status, etc.) can be misinterpreted and lead people to expect things that happened for other people instead of expecting things that are promised in Scripture.
Overall, some good stuff in this book, I would encourage reading in prayerfully and with discernment to distinguish biblical absolutes from personal experience.