Jane arrives at Thornfield months before she actually meets Mr. Rochester as indicated in Chapter 12 when the narrator states, "October, November, December passed away" prior to Jane's unfortunate first encounter with Mr. Rochester (Bronte 131). This is significant because it allows the narrator and therefore the reader to contrast the atmosphere of Thornfield Hall and Jane's moods when Mr. Rochester is present compared to the months prior when he was away from his estate. This is also important foreshadowing because it supports Ms. Fairfax's claims that Rochester is very rarely in his home, which readers later learn is due to the melancholy he feels being in the same place as his captive first wife. 

Bronte, Charlotte. Jane Eyre. Barnes and Noble Classics, 2003.