The Gardiners represent the established middle class. They are a "lowly" family connection that might hurt the Bennet sisters' prospects of marrying well.
After listening sympathetically to Mrs. Bennet's outpouring of complaints, Mrs. Gardiner speaks with Elizabeth about Jane's situation. Elizabeth confirms that Jane was very much in love and swears that Bingley's departure was no accident.
Mrs. Gardiner takes the place of Mrs. Bennet in soothing and restoring the family. She represents a stronger, sympathetic, and more sensible mother figure for the girls.
Mrs. Gardiner proposes that Jane come stay with them in London to help her recovery. While Mrs. Gardiner promises that Jane and Bingley are not likely to meet, Elizabeth secretly hopes that Jane's presence nearby will rekindle Bingley's affections.
Because of their class, the Gardiners live in a very different part of town and travel in different social circles than Bingley and his family and friends.