What is the significance of the extensive discussion of Desiree's origins in the opening of the story?

At the beginning of the story, the author makes the reader aware of Desiree's questionable background. Her parentage is unknown. Armand's family is wealthy, well established, respected..... they are French aristocrats. He is expected to marry within his own social group, and although, Desiree is a well brought up young woman.... her bloodline is a mystery. This information is significant in terms of the marriage and its offspring.