I'm a writing tutor with the university I graduated from, so this is something that I hope I can help with. :)

"gravesparker" has made excellent suggestions and I would augment his/her suggestions by making one of my own: try reading every sentence aloud to yourself. Sounds stupid and may be embarrassing, but you can find a crap-ton of grammatical errors if you do so. It's worked for me for years and it's something I recommend to my students.

Your introduction feels too short and abrupt. May I suggest taking your time with the introduction and not being in such a rush? For instance, explain in a little broader detail (because you go into deeper detail later in the essay) about what you mean by "To Kill a Mockingbird" being a motif of empathy? What can you offer to support that supposition?

This is on the nit-picky side, but what is your citation style for this essay? If you ever need to find a reference point for citation styles, this is a good place to go: http://owl.english.purdue.edu/owl/search.php. I refer my students to it and I refer myself to it on a regular basis.

I hope that my comments have helped and not hurt -- I would never want to hurt anyone. If you think I should be more specific about something I've said, please let me know. :)

Best of luck to you. :)