The idea that Lamb drives at in "Grace Before Meat" is that the rich have no spiritual nobility, even if they are part of the social class generally considered noble. While this is to some extent verbal irony, as the rich lack the very thing that their social class is called, what Lamb is driving at is a more essential, dramatic irony, that they do not in fact embody said nobility since they don't live lives that engender it.
The Burned Pig is Delicious (Situational Irony)
In one of Lamb's funnier moments, he constructs a story about the first time humans ate roast pig wherein a boy burns his house down and finds out that the pig that has died in the fire is in fact delicious. It's ironic that only through accident would people find out that cooked meat tastes good, much less that the family would have to keep this a secret until eventually going to court for eating the animal. Lamb revels in the absurdity of this irony.
The Myth of the South-Sea House (Dramatic Irony)
At the end of "The South-Sea House," Elia reveals that all of the characters that he was telling stories of were total fabrications. It's not ironic in and of itself that Elia fabricated these people, but it is ironic given the fact that the South Sea House ran a famous scam that Elia would make up fabrications about the bank similar to the fabrications the bank sold its investors.
Beat Up Books Are Better (Verbal Irony)
Elia makes the intentionally confounding statement in "Detached Thoughts on Books and Reading" that beat-up books are preferable to pristine editions, but explains the irony as the fact that a book that looks worn out has been well-read, and is therefore a better book than one which looks totally unread.
Charles Lamb: Essays Questions and Answers
The Question and Answer section for Charles Lamb: Essays is a great
resource to ask questions, find answers, and discuss the novel.