Answer:
Jane declined St. John's offer to travel to India because it will only serve his own interest and nothing for herself. Also, she did not really love him but rather look him as a brotherly figure.
Explanation:
"Jane Eyre" by Charlotte Bronte narrates the story of Jane from childhood till she becomes a full grown woman and married.
St. John is her long lost cousin who had asked him to marry him. He had also asked her to accompany him to India as his wife as he is a missionary. He kept on trying to persuade her, which she refuses as kindly as she could possibly can. But this kind refusal only strengthens his resolve. He unyieldingly persists on his attempts, sometimes bitterly telling her about the plans and her life if she stays back. Diana also told her that if she accompanies him, it will only serve his own purpose and is of nothing meaningful for Jane. For John only considers her as a tool for his missionary purpose. When he prays for her during dinner, such is his eloquence of speech and talking that Jane was almost persuaded to give in to his proposal. But then she thought she heard the voice of Mr. Rochester calling her name. It made her believe that some unnatural thing had happened and she finally got over the spell of St. John's eloquence and persuasiveness. Moreover, Jane had always regarded him as a brother and not as a lover or even husband.
