What views on marriage does Charlotte Bronte present in her novel Jane Eyre?

Charlotte Bronte, through her character Jane Eyre, shows a strong belief in the sanctity of a legal marriage. To Jane the marriage bond is not merely a convenience but a sacred trust. Therefore, when she finds out that Rochester, who is ready to marry her, is already married, she reacts with horror. From Jane's standpoint, it simply is not right to engage in a bigamous marriage, even if Bertha is insane. In Jane's eyes, one marries for better or for worse, and Bertha's condition in no way alleviates Rochester of his responsibilities toward Bertha as her husband.
Jane reveals her strong moral fiber in rejecting Rochester when she finds out he is already married. She loves him deeply, and it would be easy to rationalize his relationship with Bertha as something other than a real marriage. It would also be easy to ignore a first marriage that few people even know exists. Nevertheless, Jane will not do this. She flees Rochester instead of compromising herself with a false bond.

Bronte (and Jane Eyre) believed that marriage should be a match between intellectual and spiritual equals. One of the things that made marriage difficult for Jane was the power (legal and sexual) it gave the husband over the wife. You can see these issues at work in the section towards the end of the book where Jane has to decide if she will marry St John: on the one hand, St John appeals to her sense of duty and self sacrifice, but ultimately she rejects him because of his evident pride, arrogance, and sense of superiority. Rochester, in contrast, has actually been trapped in a bad marriage; Bertha's power over him -- her existence! -- ruins his hope for "true love" with Jane. Rochester clearly does not consider Bertha to be his wife in any real way, but is unable to escape the legal and moral bonds of marriage. In a sense, Rochester has lived the experience Jane avoids with St John -- servitude to an unloving spouse. Jane ultimately marries Rochester because she believes that they are spiritual and intellectual equals -- Rochester, in his crippled state at the end of of the book, requires Jane's care, but Jane, for her part, requires Rochester's understanding.