The above excerpt from Susan's letter to Michael is both confession and a plea. When Michael and Susan were reunited, Susan allowed him to believe that Elizabeth-Jane was their daughter, but she was not. Their own daughter died soon after Michael sold them, and Elizabeth-Jane was the daughter of another man. Above all, Susan wanted her daughter to have security before Michael became aware of this secret. This was the reason the letter was not to be opened until the day Elizabeth-Jane was to be married.
From the text:
For the good of all three of us I have kept one thing a secret from you till now. I hope you will understand why; I think you will; though perhaps you may not forgive me. But, dear Michael, I have done it for the best. I shall be in my grave when you read this, and Elizabeth-Jane will have a home. Don’t curse me Mike—think of how I was situated. I can hardly write it, but here it is. Elizabeth-Jane is not your Elizabeth-Jane—the child who was in my arms when you sold me. No; she died three months after that, and this living one is my other husband’s. I christened her by the same name we had given to the first, and she filled up the ache I felt at the other’s loss. Michael, I am dying, and I might have held my tongue; but I could not. Tell her husband of this or not, as you may judge; and forgive, if you can, a woman you once deeply wronged, as she forgives you.