Why does Malcolm test Macduff?
In Act IV, scene iii, Malcolm tests Macduff's character. Macduff has just been told that Macbeth has murdered his wife and children and has ample cause to seek personal revenge. As the heir apparent to the throne, Malcolm tells Macduff that once he is Scotland's king, he will strip the nobles of their estates and perform other tyrannical acts. In response, Macduff does not abandon Malcolm's cause but instead grieves for his country. Malcolm then reveals his intention to restore just rule to Scotland. On one level, this test of Macduff's loyalty is meant to determine the strength of the hero's commitment to the campaign against Macbeth, Malcolm noting that Macduff once "loved" his fellow-in-arms, Macbeth. But more importantly, it establishes Macduff's motivation in the battle against Macbeth as a matter of patriotism rather than private vengeance.