in to kill a mockingbird, chapter 13, scout says "I know what he was trying to do, but he was only a man". what was attics trying to do?

Atticus is trying to change the perceptions and bigotry of a town. Changing attitudes ingrained over centuries and still raw from the Civil War is a herculean thing to do.

But why does it say it right after this line that it would take a woman to do this kind of work?

I believe you're over thinking the statement. Scout isn't referring to men or women in the statement, but rather humanity. There is only so much a "person" can do, and in this particular instance that person was a man.

But why does it say it right after this line that it would take a woman to do this kind of work?