No kind action ever stopped with itself. Fecundity belongs to it in its own right. One kind action leads to another. By one we commit ourselves to more than one. Our example is followed. The single act of kindness throws out roots in all directions, and the roots spring up and make fresh trees, and the rapidity of the growth is equal to its extent. But this fertility is not confined to ourselves, or to others who may be kind to the same person to whom we have been kind. It is chiefly to be found in the person himself whom we have benefited. This is the greatest work which kindness does to others, that it makes them kind themselves.

"On Kindness in General", Spiritual Conferences (1860).