Karuna is a Sanskrit word and is used in Hinduism and Buddhism. It is translanted to mean any action that is taken to diminish the suffering of others and could also be translated as "compassionate action." When individuals experience enlightenment, they report that all beings are known as one. Therefore, it is natural to extend compassionate action or Karuna to everyone without distinction because we are all one. As we help others and aid them in their healing process, all beings benefit. Because of the oneness of all beings, it is understood that Karuna is not only extended to others out of love, but also because it is an entirely logical thing to do. In the same way that you would want to heal your own wounds, you would also want the wounds of others to heal. It is also stated in the Buddhist literature that Karuna must be accompanied by parjna or wisdom in order to have the right effect.
Karuna is the motivating quality of all enlightened beings who are working to end suffering on Earth. They continually send an unlimited amount of healing energy and guidance to us, but not all are receptive to it. As you develop Karuna in yourself, not only are you helping others, but you also become more receptive to the Karuna that is being sent by all enlightened beings. Thus your healing is quickened as well.