The English Channel is significant to Jane Eyre because it represents the distance between Mr. Rochester and Jane Eyre emotionally. Both times it is mentioned in the story, it is used as a long distance that Jane and Mr. Rochester are on opposite sides of, showing how disconnected they are at different points in the story.
This information comes from both chapters 23 and 36 of Jane Eyre. The first time it is mentioned in chapter 23, it is by Mr. Rochester stating that the distance of the English Channel would destroy the interminable love that he and Jane have for each other, that she would forget him in time. The second time in chapter 36 it is mentioned, it is in Jane's thoughts, worried that Mr. Rochester has gone a long way away. Both mentions of the English Channel are in relation to Mr. Rochester and Jane Eyre's bond, and one of them leaving to snap those bonds.
This location illustrates the limits of first-person narration because only Jane's perspective on her location and choices is shown. In chapter 23, Jane's perspective on why she needs to leave Thornfield is why her and Mr. Rochester are disconnected as far as the distance of the English Channel, and while Mr. Rochester's words are shown his emotional distance can only be inferred. In chapter 36, Jane is simply theorizing how far away Mr. Rochester is, not only physically but emotionally too, that he and her are actually too far away to be together again. However, this is a limitation of her perspective because they eventually do find each other again, and Jane is simply overthinking in this section.
Mapping this location on COVE reveals how the novel's real geography grounds its atmosphere. Seeing the English Channel's wide expanse on COVE shows just how long the distance between the characters would've been if they were on opposite sides of it, especially with the limited technology of the time.
Research: https://www.cam.ac.uk/research/features/the-channel-a-historians-view-of-an-iconic-stretch-of-water
Research (2): https://www.britannica.com/place/English-Channel
Image (2): https://www.britannica.com/place/English-Channel#/media/1/187921/611