In the final episode of season 6 of Game of Thrones Cersei is being put on trial. Why was she being tried if she had already done the walk of atonement?
Cersei was charged with many sins:
- An incestuous relationship with her cousin Lancel Lannister
- An incestuous relationship with her brother Jaime Lannister
- Possibly regicide - the murder of former King Robert Baratheon
Cersei eventually admits guilty to the first charge - a sexual relationship with Lancel.
Since this is her first step to righteousness, the High Sparrow allows her to return to the Red Keep to see her son, but as punishment, she must endure the Walk of Atonement.
Cersei must still stand trial for her other sins.
The only formal charge we hear is the one about Lancel to which Cersei eventually admits to. While we don't quite hear other charges formally I do think that they might be implied.
- The High Sparrow questions Cersei about other men she may have laid with, aside from Lancel. When she denies this, the High Sparrow doubts her answer, saying that he has heard that her children are bastards born of incest (hinting at her brother Jaime).
- While there isn't specific mention of regicide, the High Sparrow tells Cersei that Brother Lancel told them "all sorts of secrets" which implies everything. Brother Lancel presumably told them every possible secret he knows. In an earlier episode, Brother Lancel confronts Cersei to apologise for what he did to King Robert - i.e. gave him excess amounts of wine which caused a hunting accident.
- The High Sparrow keeps telling Cersei that all will be revealed at the trial and that she has "many other sins" to confess.
- During the initial questioning of the Tyrells, the High Sparrow knew an awful lot. This demonstrates that the Sparrows really do seem to have found many secrets. I'd apply this to Cersei's situation and suggest that they probably know a lot about her.
From this, I concluded that the Sparrows probably know or suspect Cersei of many more sins. Hence her trial.