What is the importance of plotting in Act III, Scene 1 of Macbeth?

In Act III, Scene I, we see Macbeth mirroring the goading of his wife in his bid to see Banquo murdered. In plotting Banquo's death, Macbeth uses the same tactics his wife utilized in encouraging the murder King Duncan. Plotting requires a ruthlessness Macbeth had not exhibited earlier in the text. He has to convince, justify and plan Banquo's murder, so the act will not arouse suspicion.