The Question and Answer section for Macbeth is a great resource to ask questions, find answers, and discuss the novel.
According to Malcolm, KIng Edward has a "healing touch" that can counter Macbeth's evil. Malcolm claims he has seen King Edward heal the sick,
A most miraculous work in this good king, Which often since my here-remain in England I have seen him...
After Malcolm lists his vices, Macduff tells him that if his words are true, it's time for him to leave Scotland, as there's no one left to properly rule. Malcolm deceived Macduff in order to test him.