In lines 23-24 Malcolm states, "Though all things foul would wear the brows of grace/Yet grace must still look so." Additionally, in lines 230-231...
...Macduff states, "O, I could play the woman with mine eyes/And braggart with my tongue!" What is the theme/motif in these lines?
These lines represent the theme initiated by the witches in the opening scene of the play with their chanting, "Fair is foul and foul is fair." What looks good may be evil, and what appears to be evil may be good. More often than not, however, this theme of the confusion between appearance and reality is demonstrated by the first part.
In numerous examples Shakespeare has his characters make comments that reveal this theme. Lady Macbeth advises her husband to "look like the innocent flower/But be the serpent under it," and Macbeth declares, "False face must hide/What false heart does know." The idea in these lines is that one must appear to be good in order to hide the evil lurking beneath the facade. The Macbeths must conceal their plans to murder Duncan when he arrives at their home Inverness so that they won't give anything away. They must be successful, they believe, so that the witches' prophecy that Macbeth will become king. The witches' prophecy, however, is another example of the theme--though this time from the opposite angle.
Although Macbeth perceives the prophecies to be positive, in the end because he murders Duncan to become king, the prophecy has a fatal result. Yes, he becomes king, but neither he nor Lady Macbeth is happy, and ultimately both die. In this case what appeared to be good ("fair is foul") was actually bad.