Merlin Carothers fifteen books are a personal testimony of his walk with the Lord Jesus Christ over a period of approximately sixty-five years. His purpose in writing is to help others by describing what the Lord has taught him along the way.
Merlin has had a very eventful and interesting life. When he shares about his life in his books it is always interesting to read, even from a purely human-interest point of view. However his purpose in sharing it is always to illustrate a spiritual principle the Lord has taught him through experience.
I don't recall or know of any author better qualified, in my opinion, to teach principles of Christianity. He describes himself with total honesty (just like the Apostle Paul), and speaks with convincing authority. I think this must be the key to his ability to write down what the Lord has taught him. He is one of those "hundred-per-cent" people - you know, like John Glenn (the first American and the second man into space).
Because of the biograpical and personal growth aspects of his writings I think it is best to read his books in the order they were written, beginning with "Prison to Praise" (1970), up to "God's Secret Weapon" (2005).