What do we learn about Eliza and Georgiana Reed and why did Bronte bring them back into the novel later ?

Eliza and Georgiana are Jane's cousins at Gateshead, the home of Jane's aunt, Mrs. Reed. As a poor dependent, Jane is constantly tomented by the Reed children, especially the brother, and heir, John. Eliza is the clever one; she is the one who instantly knows that Jane is hiding in the window seat in Chapter 1, while Geogiana is the pretty one, spoiled by her mother. Mrs. Reed says that Jane is "not worthy of...

Eliza and Georgiana are Jane's cousins at Gateshead, the home of Jane's aunt, Mrs. Reed. As a poor dependent, Jane is constantly tomented by the Reed children, especially the brother, and heir, John. Eliza is the clever one; she is the one who instantly knows that Jane is hiding in the window seat in Chapter 1, while Geogiana is the pretty one, spoiled by her mother. Mrs. Reed says that Jane is "not worthy of their notice," because of her temper and her abilty at age 10 to stand up for herself. She is soon sent away to school, and we hear nothing more of Mrs. Reed and her family until much later,  in Chapter 21, when Mrs. Reed, on her death bed following the dissipated death of John, summons Jane from Thornfield. 

What we learn about these characters from this second meeting is that their lives have moved along a clearly defined trajectory. Eliza, "very thin too, with a sallow face and severe mien," has become even more flinty with age, seeking more than anything else to become a nun and be left alone. Georgiana, "a full- blown, very plump damsel, fair as waxwork," always the flirt, has become fat and made a poor marriage. In fact, Jane's return serves to show how far she has progressed, emotionally and spiritually, compared to her cousins. As Jane says, "Eliza did not mortify, nor Georgiana ruffle me. The fact was, I had other things to think about."