The theme of this story centers around the American Revolution. When Rip falls asleep, he is living in a British colony. When he awakens 20 years later, he is living in a brand new country, the United States of America. The picture over his favorite tavern has changed from that of King George to George Washington. Now, men seem more politically aware and Rip overhears them debating politics. But, the more things change, the more they stay the same. Rip almost gets in trouble for saying he is loyal to the king (before he figures out what has happened to him), but he soon slips back into the lazy ways that he followed before falling asleep.
Rip also awakens to another type of independance: his wife has died. He notices that the house is not clean anymore like it was when she was alive, but he is happier to be free of her constant bickering. They did not have a good marriage. He was lazy and she was always yelling at him for being lazy. So, marital conflict is another theme.
You can read a discussion of the themes of this story here on enotes.