Compassion is the best protection; it is also, as the great masters of the past have always known, the source of all healing. Suppose you have a disease such as cancer or AIDS. By taking on the sickness of those suffering like you, in addition to your own pain, with a mind full of compassion, you will—beyond any doubt—purify the past negative karma that is the cause, now and in the future, of the continuation of your suffering.
In Tibet there have been many extraordinary cases of people who, when they heard they were dying of a terminal illness, gave away everything they had and went to the cemetery to die. There they practiced taking on the suffering of others; and what is amazing is that instead of dying, they returned home, fully healed.