Great Expectations Questions

So far the book is kind of confusing. One of the parts I didn't get was when Mr. Wopsle said "Swine were the companions of the prodigal. The gluttony of swine is put before us as an example to the young." But then what I didn't understand even more was when he continued "What is detestable in a pig is more detestable in a boy." (pg. 25). I think he's complaining about how all the children in those days were ungrateful but I don't understand the last part of what he said at all. Does he mean that children are sloppy like pigs? Or worthless? Or just ungrateful? I'm really confused about that and it seems like that could be an important metaphor, so help would be awesome.