Macbeth does not believe that Malcolm cannot harm himself. He is quite prepared to believe that Malcolm might harm Malcolm, which is what "harm himself" means. Macbeth does believe that Malcolm cannot harm him (i.e. Macbeth) because Malcolm's mother was apparently a woman and the witches said that none of woman born could harm Macbeth.
It gives the impression that Macbeth is superhumanly evil, as if he were the devil.
Macbeth says it, when he's contemplating the witches' prophecy.
The apparition told him that he could not be defeated until Birnam Wood came to Dunsinane Hill. Macbeth assumes that that is never going to happen, so Malcolm cannot defeat him no matter how large his army is.
Macbeth cannot get away from his evil; it is a part of him.
Macbeth
Macbeth is not worried about Malcolm and the army because he believes in the witches' prophecies that "none of woman born shall harm Macbeth" and "Macbeth shall never vanquished be until Great Birnam Wood to high Dunsinane Hill shall come against him." These prophecies give him false confidence and a sense of invincibility.
Macbeth says "it cannot be ill" because he believes that as long as he is carrying out the murder of Duncan with determination and commitment, there is no reason for it to be viewed as wrong or evil. He convinces himself that ambition and power are driving forces that justify his actions.
Lady Macbeth is excited about it. Macbeth is of two minds: "This supernatural soliciting cannot be bad; cannot be good."
Macbeth believes he is invincible because of the witches' prophecy that "none of woman born shall harm Macbeth." He interprets this to mean that he cannot be killed by any man. This overconfidence and misplaced trust in the witches' prophecy lead him to underestimate his opponents.
It gives the impression that Macbeth is superhumanly evil, as if he were the devil.
Macbeth says it, when he's contemplating the witches' prophecy.
The apparition told him that he could not be defeated until Birnam Wood came to Dunsinane Hill. Macbeth assumes that that is never going to happen, so Malcolm cannot defeat him no matter how large his army is.
Lady Macbeth uses Macbeth. She convinces him that he cannot wait for Fate to take its natural course. He must intervene to make things fir the prophecy; he must kill the king and frame his sons to make himself the heir to the throne.
Macbeth cannot get away from his evil; it is a part of him.
Macbeth
The massacre of an entire household is the revenge that Macduff cannot get on Macbeth.Specifically, Macbeth orders the murder of all inhabitants of Macduff's castle. Macduff suspects that Macbeth's actions are headed in that direction. So he escapes death by fleeing across the border between Scotland and England. He leaves behind his possessions and household, including his wife and family. In England, Macduff learns that there are no Macduff survivors other than himself in the aftermath of Macbeth's raid.Ultimately, Macduff fights and kills his sovereign. But Macbeth's Lady already dies at her own hands, Macbeth appears to have no descendants, and Macbeth's supporters desert to the combined armies of the invading English and disgruntled Scots.
Lady Macbeth places the bloody daggers near the alleged murderers in Macbeth to frame them for King Duncan's murder.