Macduff stands out from a large cast of secondary characters because of the particular harm that Macbeth does to him, and the revenge Macduff takes on Macbeth in turn. At the beginning of the play, Macduff is a loyal and brave noble fighting on Duncan’s side. He immediately distrusts Macbeth’s claim that Duncan was killed by his servants, and refuses to go to Macbeth’s coronation.
Once Macbeth understands that Macduff will not be loyal to him, Macduff becomes a particular focus of Macbeth’s anger, guilt, and rabid desire to protect his power. Macbeth arranges for murderers to kill Macduff’s wife and children, after Macduff has already fled to England to seek help from the king for his cause against Macbeth.
Macduff’s decision to abandon his family is never fully explained, and seems hard to justify, given their brutal murders. But Macduff is deeply motivated by his wife and sons’ deaths, and he speaks several times in the play about how he must revenge them. Thus, his mission to place Malcolm on the throne of Scotland is one that reflects his desire to have the true monarch ruling, but also shows his desire for vengeance for his wife and son’s murder.