"Angels are bright still, though the brightest fell;"
A4S3
• Throughout this scene Malcolm test Macduff’s loyalty and intentions.
• Malcolm isn’t yet ready to place his complete trust in Macduff - does not have flaws of Duncan. Macduff appears to be good, he concedes, but everything evil tries to wear the disguise of good. However, Malcolm says that looking good doesn’t mean you are evil, because good people also look good.
• The “brightest” is a metaphor for Lucifer, the once brightest angel who rebelled against God and became the Devil, which alludes to Macbeth who transformed from a "noble" warrior who fought for God and good, to a tyrant.