Question

What part does lady Macbeth play in Macbeths decision to kill the king

Answer 1

She calls Macbeth weak and cowardly until he finally agrees to her plan to kill the king.

Answer 2

Lady Macbeth is an example of pure ambition in the play.  She, and not her husband, is the mastermind behind the plot to kill the king.  Lady Macbeth comes up with the plan to murder the king once she discovers that he will be a guest in her home.