Brave New World takes place in a controlled environment where technology has essentially eliminated suffering, and where a widely-used narcotic dulls whatever momentary pains may arise. It soon becomes clear, however, that suffering is a part of the human experience. Without it, the citizens are somehow less-than-human. Self-inflicted pain becomes, for one character, a way to regain his humanity as well as a spiritual cleansing. God, he explains, is a reason for self-denial. This is of course tied to the notion of an afterlife: denying the body in this life will be good for the soul in the afterlife. Christianity especially espouses this theory, as suffering for one's sins is one way to emulate Jesus Christ.
Despite John's adamant convictions, suffering serves no purpose in Brave New World.
Inflicting pain on oneself is the only path to liberty in Brave New World.