The book is simple and profound at the same time. It's basic premise is to find your greatest value and to see it as your place of vocation.
He states that there are 3 stages in finding your mission in life. The first is to connect with your God; the second is to do what you can to make the world a better place. My favorite is the third phase: a)"execise that Talent which you particulary came to earth to use -- your greatest gift which you most delight to use". b)"in the place(s) or setting(s) which God has caued to appeal to you and the most" and c) and for the purposes which God most needs to have done in the world".
I do not see what some reviewers have stated that it boiled down to waiting on some inspiration or spiritual leading. I especially liked the example of being as medical doctor and working in a leper colony. It has to be a match that is helpful for both sides or you will not be happy and will have missed your mission in life.