The two earliest flashbacks in the novel and arguably the most important in regards to establishing Edna's character both reveal a depth to Edna's character that would be missing without them. Both flashbacks occur in chapter 7. In the first one, Edna is talking to Robert and recalls a "summer day in Kentucky, of a meadow that seemed as big as the ocean." When they talk about the experience, Edna tells him that when she walked in the field it felt like swimming and that "I was a little unthinking child in those days, just following a misleading impulse without question" and she suggests that she was likely "running away from prayers, from the [gloomy] Presbyterian service." This memory reveals to us that Edna's interest in running away and being engulfed by something larger than itself has its manifestations in her childhood and is not something that she is just starting to consider as an unhappy wife and mother in Creole New Orleans. She isn't that simple.
As the chapter progresses we learn that Edna had some "loves" in her past, but that they were more of her imagination than any possibility of reality. She loved a "sad-eyed cavalry officer" who was actually more of an acquaintance of her father. She loved a man, from a distance, who hardly knew she existed and who was engaged to the lady on the neighboring plantation. She finally loved a "great tragedian" that "began to haunt her imagination and stir her senses." Unfortunately, he was completely out of her realm -- a picture on her table -- and it was completely hopeless. With all of this flashback information, it comes as no surprise then that when Leonce woos her with real, actual ardor, she is taken in, even though she doesn't love him. Leonce is everything her father isn't, and that is part of his appeal. He is attentive and loving; her father is aloof and a heavy drinker. Leonce is polished and sincere; her father is a former army officer and a bit more brash. Edna even openly admits that the fact that Leonce is Catholic and that that would irritate her father is one of the reasons she agreed to marry him. This flashback gives us a very complete picture of Edna's history in regards to men and establishes the foundations of her marriage to Leonce, so that when we see things falling apart, we can know that this might have been inevitable. This has a great effect on the reading of the novel -- it makes Edna's character more complex and more interesting.