I thoroughly enjoyed reading this book for the chief reason that Dr. Sproul reveals his love and passion for prayer. He is widely known for his theological expertise and academic flair. From the books I have read of his thus far, all are dominantly written with a very scholarly imprint. His third book in the Crucial Questions series drastically differs in that his writing seems rooted in his powerfully undeniable experience with prayer. I believe this is somewhat purposeful as God did not create prayer to be a scientific entity. There will be no scientific proof of the power and work of prayer for those seeking such. Prayer is only experienced through true faith in Christ. Thus the results, success, failure, etc. of prayer can only be explained through faith experience and scripture.
Each chapter distinguishes specific aspects of prayer: The Place of Prayer, The Purpose of Prayer, The Pattern of Prayer, The Practice of Prayer, The Prohibitions of Prayer, and The Power of Prayer. The last chapter was my favorite. He expounds on several examples through Scripture to reveal the power of prayer.
I loved that he humbly admitted he does not know everything about prayer, thus a reason to continually seek the Lord through prayer.
I'm not convinced that a non-believer would gain anything from this book. But those who are already seeking the Lord may realize a more intense thirst for prayer and the work God accomplishes through it.