Jane Eyre is a dense book, and the previous educator was correct to point to the themes of class structure, the voice of women in life and literature, and more. Yet perhaps the main theme, the theme which is most pervasive and potent in this novel, is that of self-truth.
Throughout the course of her life, Jane first struggles to find self-worth, and then to maintain that worth, her integrity. Jane wants to consider herself a forthright, hardworking, honest person who is, above all, true to her self and her beliefs. Romance, abuse, rage, despair, and isolation, in turn, challenge her sense of self. Yet, each time she faces a challenge, she forges a path always towards her beliefs, her independence, and what she believes to be her good and decent qualities.
For example, when she initially becomes entangled in romantic interests between Rochester and Blanche Ingram, she does not fuel petty feelings toward either party. She does not resent Rochester for having the attention of another woman, or turn jealous and resentful of Blanche for being that woman. Rather, she turns a critical eye to herself.
Listen, then, Jane Eyre, to your sentence: to-morrow, place the glass before you, and draw in chalk your own picture, faithfully, without softening one defect; omit no harsh line, smooth away no displeasing irregularity; write under it, "Portrait of a Governess, disconnected, poor, and plain."
Jane uses her artistic talents to sketch a self-portrait, to remind herself in keen detail who she is as a person. On the one hand, she genuinely believes herself at this time to not be worthy of Rochester's affections. She also does not value material things, nor pandering to her own vanity. She affirms all of these truths to herself by rendering herself pictorially, with brutal honesty. This honesty, this truth to self, will one day be one of the characteristics which so strongly compels Rochester. Even as she prepares for her wedding to Rochester, she chooses a plain dress and does not adorn jewelry as it would "seem strange for Jane Eyre."
We also see Jane wrestle with her beliefs and sense of self in a much more dramatic fashion after the previously mentioned wedding. Once she discovers Rochester is already married to an "insane" person housed in the estate, she flees. Before doing so, she has a heart-wrenching conversation with Rochester, in which she wants to succumb and love him, but resolves that the deception and hypocrisy of her staying would be too great. She reasons with herself:
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. Laws and principles are not for the times when there is no temptation: they are for such moments as this, when body and soul rise in mutiny against their rigour; stringent are they; inviolate they shall be. If at my individual convenience I might break them, what would be their worth? They have a worth—so I have always believed; and if I cannot believe it now, it is because I am insane—quite insane: with my veins running fire, and my heart beating faster than I can count its throbs. Preconceived opinions, foregone determinations, are all I have at this hour to stand by: there I plant my foot."
A great deal happens even after this climactic episode, and at every juncture, Jane Eyre does her utmost to stick to her principles. She values self-respect, self-truth, and she is not willing to compromise it even for those things she desires most. Truth to self is valued above all else. This, in short, is the central theme of this novel, and the underpinning of Jane's character.