Seneca on gratefulness and generosity.

We should try by all means to be as grateful as possible. For gratitude is a good thing for ourselves, in a sense in which justice, that is commonly supposed to concern other persons, is not; gratitude returns in large measure unto itself. There is not a man who, when he has benefited his neighbor, has not benefited himself, — I do not mean for the reason that he whom you have aided will desire to aid you, or that he whom you have defended will desire to protect you, or that an example of good conduct returns in a circle to benefit the doer, just as examples of bad conduct recoil upon their authors, and as men find no pity if they suffer wrongs which they themselves have demonstrated the possibility of committing; but that the reward for all the virtues lies in the virtues themselves. For they are not practiced with a view to recompense; the wages of a good deed is to have done it. I am grateful, not in order that my neighbor, provoked by the earlier act of kindness, may be more ready to benefit me, but simply in order that I may perform a most pleasant and beautiful act; I feel grateful, not because it profits me, but because it pleases me.