I picked this from my wife's bookshelve when I first got married. This is perhaps one of the best books I read on preparing as a missionary for a long time. I always learn a lot from Oswald Chambers' writings. I read his devotions, My Utmost for His Highest, on a daily basis.
This book is deep and solid. Some of the thoughts and wisdom behind it is so deep that there are times I have no idea what he is trying to say. At the same time, I am always thirsting for more.
I highly recommend this book for anyone who is serious in follow Jesus. I don't think this book is particularly for missionaries. Though, missionaries will find this book helpful in them be fueled by the Holy Spirit and not by might.