There is a sense in which this hilarious tale can be read as something of a cutting commentary about American society in the time of writing. Note the way in which Easterners are presented as being sophisticated and knowledgeable and Westerners lack an education and are gullible, at least at surface level. Yet Twain does this to explore these national stereotypes more deeply by exchanging the roles. The Easterner (the narrator), is a snob who is gullible and easily tricked, whilst the Westerner (Simon Wheeler) is someone who, whilst he lacks the formal education of the narrator, nevertheless shows himself to be more intelligent and has the ability to narrate and recount hilarious tales.
The tale within the tale also would have had certain significance for Twain's readership. Daniel Webster was a famous American statesman known for his rhetoric. Andrew Jackson was a former president was a firm advocate of democracy and rights for everyone. The use of these allusions show that the kind of picture of Americans that Twain was presenting was one that had many different angles to it: Americans are depicted as having the ability to be practical, resourceful and determined (traits that arguably Americans are famous for), whilst at the same time naive, narrow-minded and easily tricked.
Davide, your answer is simple. Gambling is bad.