Jane Eyre has these thoughts as she reenters Thornfield after an early evening walk. On this walk to mail a letter, she had encountered a strange man who had been thrown from his horse, sprained his ankle, and needed her help to get back on horseback. Little did she know it was Mr. Rochester, her employer. Her feelings, instead, were aroused by the pleasure in being able to do something useful for an unknown, injured man.
She dislikes returning to Thornfield because she has too little to do there. Being Adele's governess doesn't take up enough of her time, and she has become restless and bored with the quietude of her life. In the passage above, she is saying that she would have benefitted by having some more struggles and challenges—these, the "storms" of life, would have invigorated her and done her "good." She then likens her desire for challenges to a man who has been sitting too long in a comfortable chair, wanting a vigorous walk. She says,
Just as natural was the wish to stir, under my circumstances, as it would be under his.
This tells us that Jane is the type of person who thrives on struggles, excitement, and the fulfillment of being needed. She likes an active life. She is also communicating in this passage, as she does elsewhere, that despite what Victorian society might say about a woman's place being in the home, many women need more stimulation and action than a placid homelife brings.
This ties in with two major themes of the novel. The first is that we grow, mature, and find fulfillment in being challenged and through helping others. For example, though Lowood School is a difficult place to be, the adversities of it help Jane grow stronger and bond her to other people there. Likewise, she now knows she needs some hardship to feel fully alive. Second, the above passage ties in with the feminist theme of the novel: Brontë asserts repeatedly that the active life is not just for men but a deep-seated need for women as well.