In addition to the posts of Riccardo Faucci and Paul Turpin, for an  excellent discussion of Smith's concept of sympathy, you will find very useful the chapter on Ethics in D. D. Raphael's _Adam Smith_(Oxford University Press, 1985) and also perhaps the chapter titled Comparisons.
 
Raphael explains with painstaking details how Smith idea of sympathy is unique (not to be confused with the usual meaning, although Smith himself sometimes slips into such usage) and is linked to moral judgment, not moral sense. For him, sympathy in the sense of correspondence of feelings between individuals, creates a social bond. But that correspondence is based on a complex process of identifying with the other person in seeking approval for one's actions. Raphael connects it with the important concept of the 'impartial spectator' and origin of conscience, concluding that it is Smith's very significant contribution to moral psychology. He then compares it with Freud's super-ego and finds Smith's version more optimistic. I may not have captured it adequately, but found it very edifying.
 
Best, 

Sumitra Shah