"Brotherhood" as an ideal has meant different things to different men. Here the author begins by examining two contrasting views: that of the ancient mystery religions, which created 'closed' brotherhoods of the initiated; and that of the Enlightenment, which looked to a future achievement of an 'open' brotherhood of all men. The author finds the first of these views too restricted and indward-looking, and the second too extended to make hard sense. But it is crucial to his purpose that he does not reject either out of hand. After an exposition of the New Testament teaching, he proposes a synthesis in which the Christian ideal of brotherhood is shown to combine both these opposing views in a fruitful tension.