Doulos. Slave. The understanding of the true meaning behind this New Testament word will challenge you in your life as a believer in Christin a way that you never imagined.? The Doulos Principle is a fresh and inspiring look at what it means to live life as a ?Slave? (Doulos) to God.? The easy to understand concepts and clear life explanations will challenge those new to Christianity as well as those who have been walking with the Lord for years. To know the will of God and do that will.? This is the Doulos Principle.