In Jane Eyre, Jane feels a strong moral responsibility to God that she has spent years cultivating into a need to do what she sees as the right thing. These beliefs, along with her moral compass, have been perhaps the only thing that sustained her and gave her purpose throughout her difficult upbringing—that is, until Mr. Rochester came along and she fell madly in love with him. Still, there are points at which Jane seems to come to an impasse; she's not quite sure how to reconcile her love with Mr. Rochester with her desire to appease God. This is especially difficult for her, because not only is Mr. Rochester still married, which Jane finds out right before they are about to complete their own nuptials, but he keeps massive secrets from her and others about the state of his private life and his relationships. She finds these pieces of information to be in direct opposition to her own sense of morality, causing her to be confused about the choices she must make.
Near the end of Chapter 27, Jane is nearly convinced to acquiesce to Mr. Rochester's attempts to get her to stay with him, even though she has just found out about Bertha, his estranged wife: "Who in the world cares for you? or who will be injured by what you do?” Still indomitable was the reply: “I care for myself. The more solitary, the more friendless, the more unsustained I am, the more I will respect myself. I will keep the law given by God; sanctioned by man. I will hold to the principles received by me when I was sane, and not mad—as I am now." Here, Jane questions what she will do and who she will turn to, as Rochester is the only person in the world who loves her. Still, she holds tight to her beliefs and her responsibility to herself. When she leaves him, the conflict she feels about being torn from him and doing the right thing is evident:
Gentle reader, may you never feel what I then felt! May your eyes never shed such stormy, scalding, heart-wrung tears as poured from mine. May you never appeal to Heaven in prayers so hopeless and so agonized as in that hour left my lips; for never may you, like me, dread to be the instrument of evil to what you wholly love (Chapter 27).
Jane feels staying with Rochester would be seen as evil in the eyes of God, so she must leave; she has no choice in the matter.
In another passage, in Chapter 34, St. John asks for Jane's hand in marriage. As she is still in pain over Mr. Rochester, and wishes to do the good work of God, Jane almost relents. Here, we can see her inner turmoil:
"As his curate, his comrade, all would be right: I would cross oceans with him in that capacity; toil under Eastern suns, in Asian deserts with him in that office; admire and emulate his courage and devotion and vigour: accommodate quietly to his masterhood; smile undisturbed at his ineradicable ambition. . . I should suffer often, no doubt, attached to him only in this capacity."
Still, even though his ideals fit perfectly with hers, Jane doesn't think marrying St. John would be a good idea because she does not love him as she does Mr. Rochester.