Why does Claudius say that his crime hath the primal eldest curse upon't?

In Shakespeare's "Hamlet," Claudius refers to the "primal eldest curse" to acknowledge the gravity of his crime—murdering his brother, King Hamlet. This phrase evokes the biblical story of Cain and Abel, where Cain's act of fratricide brought a curse upon him. Claudius recognizes that his act of ambition and betrayal not only violates moral and familial bonds but also aligns him with the archetype of the worst kind of sin, emphasizing his guilt and the weight of his conscience.