Virtue is not said to be amiable, or to be meritorious, because it is the object of its own love, or of its own gratitude; but because it excites those sentiments in other men.
 Adam Smith, The Theory of Moral Sentiments (1759). copy citation

Context

“that is, to deserve love and to deserve reward, are the great characters of virtue; and to be odious and punishable, of vice. But all these characters have an immediate reference to the sentiments of others. Virtue is not said to be amiable, or to be meritorious, because it is the object of its own love, or of its own gratitude; but because it excites those sentiments in other men. The consciousness that it is the object of such favourable regards, is the source of that inward tranquillity and self-satisfaction with which it is naturally attended, as the suspicion of the contrary gives occasion to the torments of vice.” source