The Thornfield section is a kind of a trial for Jane, spiritual as much as carnal and sexual. Up until that point, she had never fallen in love. It happens to her now, but this love is not just another romantic love story. Her beloved is almost a ruffian, with violent fits and eccentric character - not at all handsome, but extremely passionate and therefore very sexual. Nevertheless, Jane senses a spiritual attachment to him, as her soulmate, which makes this relationship worth all the effort in her eyes.
On the other hand, Bronte juxtaposes the shiny, brilliant word of aristocratic, sensual bodies to the gloomy and stark spirituality of Jane Eyre. First of all, there is Rochester's story about his former mistress, Adele's mother, who was a beautiful, adulterous seductress. On the other hand, there is Rochester's noble company that he brings to Thornfield, particularly Blanche Ingram, who is also beautiful and apparently a very desirable match. She is Jane's absolute counterpart, and that is precisely why Rochester eventually casts her away to propose to Jane.
Here is how Jane sees her spiritual attachment to Rochester, observing him in the company of his noble friends:
"<span>He is not to them what he is to me," I thought: "he is not of their kind. I believe he is of mine;—I am sure he is,—I feel akin to him,—I understand the language of his countenance and movements: though rank and wealth sever us widely, I have something in my brain and heart, in my blood and nerves, that assimilates me mentally to him. […] I must, then, repeat continually that we are for ever sundered:—and yet, while I breathe and think I must love him."</span>
