"Unfix his earth-bound root? Sweet bodements!
Rebellion's head, rise never till the wood
Of Birnam rise, and our high-plac'd MacBeth
Shall live the lease of nature, pay his breath
To time and mortal custom. Yet my heart
Throbs to know one thing: tell me-if your art
Can tell so muich,- shall Banquo's issue ever
Reign in this kingdom?" IV, i, 95-103.
MacBeth is saying that he is a king, and all shall fear him after he confronts the witches, and different apparitions
who fortell his dead. He uses this metaphor to symbolize that he is higher than everyone else, and that he beleives
that he will die when he is meant to die, and will not be murdered. Also, perhaps by using this comparison, he will
be reasuring himself that no one wants to kill him.