In Macbeth, how do quotes that involve imagery referring to planting or harvesting make a significance to the play?
For example, when Malcolm states, "Macbeth / Is ripe for shaking, and the powers above / Put on their instruments" (4.3.278-280).
In one way, imagery relating to the earth, planting, harvesting in The Tragedy of Macbeth helps to provide a contrast to the method in which Macbeth gains the throne. After Macbeth and Banquo encounter the witches, they meet with Duncan, Malcolm, and others at Forres where Duncan heaps his admiration on the two for defeating the insurrection against his throne. During the meeting Duncan uses the planting and harvesting imagery to assure Macbeth and Banquo that he will cultivate them to a healthy condition in his realm.
Duncan. (to Macbeth) Welcome hither: I have begun to plant thee, and will labor to make thee full of growing. -- Noble Banquo, That hast no less deserv'd, nor must be known No less to have done so, let me infold thee And hold thee to my heart.
Banquo. There if I grow, The harvest is your own.
Duncan then names his son, Malcolm, Prince of Cumberland and heir to his throne, infuriating Macbeth, the next in line to the throne, and helping to set Macbeth on his course of murdering Duncan for the throne. The way of the world would be for Macbeth to follow the set course of nature, like the course of planting, tending crops to maturity, and harvesting them in plenty. But by murdering Duncan to secure the throne, Macbeth has broken the chain of life, of nature, and must suffer the consequences.
The imagery follows throughout the play with the witches and their connection with the earth, with the quote from Malcolm, with Birnam wood appearing at Dunsinane and bringing the army which will eventually set nature right with Macbeth's death, and through other instances.