[Act 5] What is the significance of Malcolm's ascension?

Finally, the mirror carried by the last king in the Show of Kings during the witches' Show of Kings in Act 4 Scene 1 represented the Stuart posterity stretching out "to th' crack of doom" (4.1.117); the the overthrow of Macbeth and the Malcolm, the rightful heir, meant not only a general purgation of the country's evil, but the establishment of a line of kings, one of whom sat in Shakespeare's audience hundreds of years later and was almost morbidly aware that the same evils continued to beset great men. The Show of Kings confirms the words of King James himself, who expressed the hope that he and his descendants would "rule over [Britain] to the end of the world," almost exactly matching the prediction of the witches.