Here is the emotional response when you don't understand those in publishing:
He not only sounds unprofessional, but a newbie and is not ready to be published. No literary agent wants to hold your hand and wipe your tears through acquisitions. Don't forget those edits too.
I beg you, don't query until your skin is ready. You might want to query that same agent another book in a year or two when you have better perspective on the industry.
Also, THINK before you respond to an agents rejection letter and then don't. If you don't have anything nice to say then shut the hell up. You're making it harder on the rest of us.
Research gives you the professional edge. Go to conferences, blog, twitter, tumblr, and get creative writing books at the library. Trust me, you can't go wrong.