Macduff feels guilty when Duncan is killed, and again when his wife and son are killed. He reacts by vowing revenge on Macbeth.
Macduff is a Scottish noble with a fiery temper. He seems to have been very close to King Duncan, so when Duncan is murdered he feels strong emotions.
O horror, horror, horror! Tongue nor heart
Cannot conceive nor name thee. (Act 2, Scene 3)
Macduff is not afraid to show his true feelings. He is an emotional man. He also seems to be the only one interested in helping Lady Macbeth when she appears to faint from the news of Duncan’s death.
Macduff seems suspicious from the start. When Ross asks him if he is going to see Macbeth crowned, he says he is going home to Fife instead. His actions and words show that he is beginning to wonder about Macbeth and who really killed Duncan.
Well, may you see things well done there, Adieu,
Lest our old robes sit easier than our new (Act 2, Scene 4)
It is actually this suspicion that leads to his family’s murder, because his actions have made Macbeth suspicious. When he goes on to join Malcolm, he leaves his wife and son behind. Macbeth has them slaughtered. This event fills Macduff with guilt, because he sees his actions as to blame. When Malcolm tells him to put his grief into anger, he says he will do so, but he will still feel it.
They were all struck for thee! Naught that I am,
Not for their own demerits, but for mine,
Fell slaughter on their souls. Heaven rest them now! (Act 3, Scene 3)
In the end, Macduff sides with Malcolm and manages to put himself in Macbeth’s path. He fights him and prevails, cutting his head off. Still, he will likely carry the guilt of what happened to Duncan and his family with him for the rest of his life.