What are some examples of verbal irony from Act III, scene vi of Macbeth?What is the point of it, and the understanding that is achieved by using...

The most obvious sort of irony in this scene is sarcasm,
used by Lennox to emphasize his distaste for Macbeth.  This is the first scene in which
Lennox appears after the ill-fated banquet scene in which Lennox observed Macbeth's
behaviour upon seeing Banquo's ghost.  Lennox and the others did not see the ghost, but
he got a pretty good idea of Macbeth's role in both Banquo's murder and the murder of
Duncan from this event.

Here are some of the ironic and
sarcastic comments that he makes:

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...The gracious
Duncan

Was pitied of Macbeth.  Marry he was
dead.

And the right-valiant Banquo walk'd too
late;

Whom you may say, if 't please you, Fleance
killed,

For Fleance fled.  Men must not walk too
late.

Who cannot want the thought how
monstrous

It was for Malcolm and
Donalbain

To kill their gracious father?  Damned
fact!

How it did grieve
Macbeth!

He goes on in ironic
sarcasm to explain how "nobly" Macbeth has behaved and that he has "borne all things
well."  Shakespeare is using this ironic sarcasm to highlight Lennox's anger and disgust
at the two-faced murderer, Macbeth.