"This is a rich and wise book, one to treasure and re-read." So says J.I. Packer and I couldn't agree more.
The big idea that Piper teaches in this book is that it is only by God's daily grace to us that we will make it from now through the rest of today and the rest of our lives and into His kingdom. Piper teaches powerfully from the bible that God has promised to give us this grace and that nothing will stop Him from keeping His promise. As we trust Him to keep that promise, faith severs the root of our sinful actions and attitudes.
What really marks this book out is that every 2 or 3 chapters of teaching about God's future grace are separated by a chapter on "applying the purifying power". These chapters deal with how to fight against sinful attitudes through faith in God's future grace. What gripped me was that many of these are the very sins that I fight daily and yet had never come across any kind of structured bible teaching on how to fight them. So Piper covers anxiety, pride, lust, bitterness, despondency and others.
There are very few Christian books that I have found so useful that I have wanted to repeatedly go back to them. This is one of those books.