The best way to answer this question is to look at how Jane decides to resist her inner desires and follow Rochester to Europe and become his mistress. Clearly, this is one of the crucial decisions that she needs to make in this excellent novel, and if we examine Chapter Twenty-Seven in particular, we can see how her values and her beliefs help her at this stage to make a wise decision and to prevent her from becoming nothing but a powerless mistress who would never be Rochester's equal. Even though Jane is friendless in the world and without family, she decides that her own sense of self-worth is still something worth fighting for:
"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?"
Note the way that again and again Jane's own moral code and set of values are refered to. They act as her compass at this point of her life when she is so overwhelmed by sadness and grief and can't think straight. In times where she is "mad" as Jane herself says she is, turning back to her set of values which she sees as being enshrined by God, provides her with guidance so that she knows what she should do.