to make way for the full strength and development of the central consciousness

Helen Burns may be taken a metaphor for an extremely optimistic, long suffering, forgiving and kind-hearted version of Jane Eyre. Or perhaps taken as a foil of that sort for Jane’s more pragmatic and realistic outlook on events and life.

On the contrary (a pole apart from Helen - polar opposites), Bertha Mason may be seen as a metaphor for an opposing metaphor of extreme of violent and unbridled female sexuality. She is convincingly placed in this distorted image of Jane by being wife to the conscientious and dutiful Mr Rochester, so that the reader is aware of her mirroring the developing, future and - ultimately - married connection between Jane and Rochester.

Helen dies in a rather “socially acceptable” Victorian way, of tuberculosis, making her an object of conventional pity; Bertha dies in a fire of her own making, with hints of the savage judgement of Fate. Thus it is that two extreme and opposing versions of womanhood (polar opposites), both of which have acted as parenthetic foils for Jane, vanish from the scene, leaving us with only Jane as a realistic sort of middle ground of femininity. Jane is left as an expression of "the full strength and development of the central consciousness" of herself.