The analyses of a text #1

The narrator recalls his childhood.
Uriah is the clerk for Mr. Wickfield who is the master of the narrator's boarding house, his grand aunt's friend, and a lawyer.
The narrator offers to teach Latin to Uriah .

"Would you like to be taught Latin?" I said, briskly. "I will teach it you with pleasure, as I learned it."
"Oh, thank you, Master Coperfield," he answered, shaking his head. "I am sure it's very kind of you to make the offer, but I am much umble to accept it."
"What nonsense, Uriash!"
"Oh, indeed you must excuse me, Master Copperfield! I am greatly obliged, and I should like it of all things, I assure you, but I am far too umble. There are people enough to tread upon me in my lowly state, without my doing outrage to their feelings by possessing learning. Learning ain't for me. A person like myself had better not aspire. If he is to get on in life, he must get on umbly, Master Copperfield."
I never saw his mouth so wide, or the creases in his cheeks so deep, as when he delivered himself of these sentiments, shaking his head all the time, and writhing modestly.
"I think you are wrong, Uriah," I said. "I dare say there are several things that I could teach you, if you would like to learn them."
"Oh, I don't doubt that, Master Copperfiled," he answered, "not int the least. But not being umbel yourself, you don't judge well, perhaps, for them that are. I won't provoke my betters with knowledge, thank you. I'm much too umble."
[David Copperfield by Charles Dickens]
1. I'd like to know what "them" and "that" refers to respectively.
2. And I'd like to know if "for them that are" means "since that are them."
Thank you in advance for your help.