It is an act of mortification, in which the practitioner learns to not be ruled by the comforts of the body and the world. John the Baptist mortified himself by wearing an uncomfortable hair shirt. To one who is unfamiliar with the practice, it can seem madness. Conforming the will through suffering and prayer can allow one to unite with Christ, who suffered for all.
The faith alone vs. faith plus works argument has been addressed ad nauseam elsewhere, so it will hardly be settled here.
