Whats the difference between sympathy and empathy?

Each person has to learn many things in his life, amongst them are feeling for justice, objectiveness and empathy. One can easily do without them, as they usually apply to others. What I mean to say is: they don't help you to be more successful, more rich or anything like that, but they are essential to the society. Without them, the society would have been a mere spectrum of robots performing their tasks and dieing out when unnecessary. Now, you don't want to live in such society, do you ?