The original question had to be edited. I would suggest that Amir's quote about Soraya reflects his own guilt about the secret he harbors in his treatment of Hassan. The quote is based on how Amir's fundamental journey is "to be good again." This is at the base of Amir's being, something that drives him and motivates him in yearning to be more than what he is. The idea of the "secret" being "out," "spoken," and "dealt with" is reference to the concealment that is a part of Amir's being before he decides to return to Afghanistan.
For Amir, the quote is reflective of the discovery and journey intrinsic to his identity. Amir's purpose in the novel is one where he is forced to come to grips with his own "secret." It is one in which he seeks to "deal with" as the novel develops. As the novel develops, Amir recognizes fully the need to be open and confront the issues of his past. This becomes a critical part of his identity, something that the journey of self- discovery makes possible. In seeing how his wife has dealt with her past, it provides a potential blueprint for Amir to deal with his. The quote illuminates such a condition.