Brotherhood means friendship. Enmity is counterproductive to achieving and preserving Brotherhood. Indeed, Brotherhood is more than friendship. To be a Brother and to be part of a genuine Brotherhood require caring enough to be concerned about more than mere friendship or mere companionship. Genuine Brotherhood imposes a special obligation between friends.
Most friendships are similar to the relationship between close neighbors.
Brotherhood is more than that. Brotherhood is caring about each other and each other's welfare. When one is only a friend of another and losses that friendship, the friend is gone. But, when one is a Brother and loses the friendship of another Brother, Brotherhood still binds them together. Genuine Brotherhood transcends the interruption of friendship.