Cry, the Beloved Country Religion Quotes

How we cite our quotes: (Book.Chapter.Paragraph)

Quote #10

— I am a weak woman, you know it. I laugh and speak carelessly. Perhaps it would help me to become a nun.
— You mean, the desire?
— Gertrude hung her head. It is that I mean, she said. (2.27.49-51)

Why is it so wrong for Gertrude to have desires? What specific criticism does Cry, the Beloved Country offer for Gertrude's desires? Gertrude also has a young son. If she chose to become a nun (as, in fact, we know she doesn't), what would be her moral obligation to him?