Claudius utters these lines at the beginning of a soliloquy in which he confesses to murdering his brother. At first Claudius does not explicitly state that he killed his brother. However, his reference to the "primal eldest curse" that has been laid on his "offence" alludes to Cain's murder of his brother, Abel, as recounted in the Bible. By comparing himself to Cain, Claudius illustrates that he understands the severity of his sin, and he expresses his sense of his own moral corruption through images of decay and putrefaction: his sin is "rank" and sends the smell of rot all the way to heaven. Additionally, Claudius's confession also gives the audience (and only the audience) confirmation that he did, in fact, kill his brother. Hamlet's apparent descent into madness might otherwise suggest that the murder conspiracy exists solely in Hamlet's head, but Claudius's confession clears this ambiguity up—but not for any of the characters in the play, sadly enough.