Medical conditions that destroy nerves — leprosy, spinal cord injury, diabetes — are among the most difficult to treat. Without a sense of touch or pain, the patient can get a bedsore by lying in the same position too long or a foot sore by wearing too-tight shoes. The body no longer warns itself of danger. According to Paul, people can develop a similar kind of moral insensitivity, which silences their consciences and hardens their hearts. That condition can prove fatal.
Taken from NIV Student Bible