O, full of scorpions is my mind, dear wife!Thou know’st that Banquo and his Fleance lives.
What’s to be done?
There’s comfort yet; they are assailable.Then be thou jocund...there shall be doneA deed of dreadful note.
Be innocent of the knowledge, dearest chuck,Till thou applaud the deed.
Thou marvel’st at my words, but hold thee still.Things bad begun make strong themselves by ill.So prithee go with me.
Macbeth confesses that knowing that Banquo and Fleance are still alive has caused his mind anguish and torture. Macbeth obsessively worries about his future as king, as Lady Macbeth attempts to calm him and reason with him. She claims that they can't live forever.
Macbeth states that knowing that Banquo and Fleance can be killed brings him comfort and joy. He indirectly reveals his plans to murder them later that night. His vague words confuse Lady Macbeth and she questions his plans. Macbeth refuses to tell her more until the deed has been committed.
Lady Macbeth begins to understand his plans and is shocked. Macbeth justifies himself claiming that once a bad deed is committed, he can't stop. He regains his composure and leads Lady Macbeth out of the room to prepare for the night's banquet.