In my opinion, the central theme in "How I Met My Husband" is difference in economic and social class and the perspective that arises from that difference. This can be most easily distinguished by observing the relationship between Mrs. Peebles and Edie. Mrs. Peebles, the wife of prominent Dr. Peebles, has a very high social-economic standing while Edie is simply her "hired girl," and only fifteen at that.
A good example of this difference in class is the incident when Edie tries on the beautiful satin gown belonging to Mrs. Peebles. Edie simply couldn't resist and then is caught in the act when Chris Watters comes to the door. Her anxiety over this incident causes her to backpedal enough in order to cover something taboo for her lower economic and social class.
Edie, because of her farm background and because of her innocence, is able to see both the goodness and the falsity in regards to people's characters. Mrs. Peebles is unable to do this, despite a life of upper middle-class advantage and a great attempt at kindness. Edie explains it quite well:
Sometimes I thought about the way we lived out at home and the way we lived here and how one way was so hard to imagine when you were living the other way.
Further, the concluded relationship between Edie and Chris proves the great divide between the classes while Edie's eventual marriage to the kindly mailman confirms that nothing has changed by the end of the story in regards to the central theme.