The inclusion of the country side as a setting for the play serves a few reason. First, it is the place from which Jack escapes under his fake persona, Ernest, to go into the city to cause havoc and live like a libertine. In the country, his serious side of "Uncle Jack" is methodological, responsible, even fatherly. Hence, the city represents the pleasures of life while the country is a representation of the bucolic, quiet, and peaceful in Jack's personality. We know, however, that Jack can only take so much of the country before escaping to the city. Much like him, Algernon runs away from the city to find his true love in Jack's estate in the country.
The second instance showing the marked different between town and country is on Act II when Cecily and Gwendolen have their famous showdown. As part of their tag-team style insults Cecily does what it takes to make Gwendolen look silly when the latter points out the silly life in the country.
GWENDOLEN:Five counties! I don't think I should like that. I hate crowds.CECILY:[Sweetly.] I suppose that is why you live in town? [GWENDOLEN bites her lip, and beats her foot nervously with her parasol.]
Moreover, Gwendolen "kindly" points out to Cecily that it is "unfashionable" to use sugar on tea, or to serve cake at teatime. In summary, the fact that Cecily is a country girl makes her automatically inferior.
Personally I cannot understand how anybody manages to exist in the country, if anybody who is anybody does. The country always bores me to death.CECILY:Ah! This is what the newspapers call agricultural depression, is it not? I believe the aristocracy are suffering very much from it just at present. It is almost an epidemic amongst them, I have been told. May I offer you some tea, Miss Fairfax?
The women declare war on each other until their issue is resolved. However, they made it clear that there is a very big gap in terms of their social standing based on their origin.