Yea exactly what John said. They have not even offered you a full-time associate job yet and you owe them nothing. If for some strange reason you don't pass the bar or the firm simply runs out of money they won't hire you later on. If you have the chance to make some money during the summer take it and get some experience. Plenty of people do not return where they worked for the summer. The whole point of working for a summer is to see if YOU like it. Of course they need to like you, but they can put you on the street at anytime and you can leave them at anytime. If it will work out for one summer then do it even if you have no intention of working there in the future.