He who can quicken the feeling of another to joy or to gratitude, by that much he adds to his own life. - Hazrat Inayat Khan

Commentary by Pir-o-Murshid Inayat Khan: Each one has his circle of influence, large or small; within his sphere so many souls and minds are involved; with his rise, they rise; with his fall, they fall. The size of a man's sphere corresponds with the extent of his sympathy, or we may say, with the size of his heart. His sympathy holds his sphere together. As his heart grows, his sphere grows; as his sympathy is withdrawn or lessened, so his sphere breaks up and scatters. If he harms those who live and move within his sphere, those dependent upon him or upon his affection, he of necessity harms himself. His house or his palace or his cottage, his satisfaction or his disgust in his environment is the creation of his own thought. Acting upon his thoughts, and also part of his own thoughts, are the thoughts of those near to him; others depress him and destroy him, or they encourage and support him, in proportion as he repels those around him by his coldness, or attracts them by his sympathy. Each individual composes the music of his own life. If he injures another, he brings disharmony. When his sphere is disturbed, he is disturbed himself, and there is a discord in the melody of his life. If he can quicken the feeling of another to joy or to gratitude, by that much he adds to his own life; he becomes himself by that much more alive. Whether conscious of it or not, his thought is affected for the better by the joy or gratitude of another, and his power and vitality increase thereby, and the music of his life grows more in harmony.    from  http://wahiduddin.net/mv2/I/I_I_2.htm