Compassion is defined in Buddhist teaching as the trembling or quivering of the heart in response to seeing pain or suffering. Alone with love and altruism, compassion can be seen as warm-heartedness replacing cynicism, beneficence taking the place of indifference, caring supplanting aloofness. The Dalai Lama, whose life has not been easy, has said, "The reason I am pretty happy is because of the force of compassion. Compassion makes me feel at one with everyone."
There is the same difference in a person before and after he or she is in love as there is in an unlighted lamp and one that is burning. The lamp was there and it was a good lamp, but now it is shedding light too and that is its real function.