In Act II of "Macbeth," it is Ross and Lennox who arrive at Macbeth's castle after Duncan is murdered. Based upon his initial survery of the king's quarters there, Lennox surmises that Macbeth's chamberlains are responsible for the murder. Then, in Act III Lennox appears again at the banquet for Macbeth. However, Macbeth is disturbed by the sight of Banquo's ghost, saying odd things and acting strange. Lady Macbeth scolds her husband for "breaking the mirth," but Macbeth expresses his fears. And, when Ross asks Macbeth of what he is afraid, Macbeth rushes and Lennox calls out,
Good night; and better health/Attend his Majesty! (III,iv, 122-123)
This line seems rather ironic, if not sarcastic, since Lennox suspects Macbeth of the murders of Duncan and Banquo. So, when he speaks in III,vi, it is with sarcasm because the others should be able to perceive the real Macbeth as Lennox does.
The gracious Duncan/Was pitied of Macbeth: marry, he was dead./And the right-valiant Banquo walked too late;/Whom you may say, if 't please you, Fleance killed,/For Fleance fled. Men must not walk too late.
Lennox urges the lord to draw his own conclusions. Macbeth has been near both Duncan and Banquo when they die; how odd, he asks sarcastically, would it have been for Malcom and Donalbain to have killed their "gracious father"? And how, asks Lennox, did Macbeth react? Has he not "borne" things well? And, continues Lennox, if Duncan's sons were here, Macbeth would show them "what it is to kill a father." Lennox simply cannot understand why the others do no perceive the evil Macbeth for the villain that he is.