The fact that Jane is an orphan connects to the theme of the search for love. However, it also connects to the theme of finding love in a way that does not compromise your individuality and integrity.
Jane is desperate to be loved, and she feels that she has never been truly loved because of her experience as an orphan. However, she is also strong and independent, and throughout the novel, she struggles to manage both desires. Jane wants to be valued for who she is, and her desire to protect herself leads her to refuse Rochester's proposal, as he would compromise her integrity. St. John, however, offers the opposite. Integrity and meaning, but no love. The need to balance out these two emotions is the driving force of the novel.