Metaphor in Macbeth
Bellona is the Roman goddess of war, making her bridegroom the god of war. The Thane of Ross uses this metaphor to praise Macbeth's unsurpassed skill on the battlefield as he confronted the Norwegian forces.
Lady Macbeth tells her husband to shore up his courage and hold it to him by using a metaphor that refers to the notch on a cross-bow that holds the taut string before firing. Lady Macbeth's metaphor is ironic because it draws a connection between Macbeth's act of selfish ambition and a soldier stringing a bow. Soldiers act on behalf of the king and country, while Macbeth acts on his own accord. In this way, Lady Macbeth not only tells him to "tighten" his courage so that they don't fail, she metaphorically elevates the purpose for his courage and justifies their actions.
In another clothing metaphor that extends from and builds on Macbeth's previous comments, Lady Macbeth accuses him of a lack of resolution to carry out the plan. Here, "hope" initially refers to Macbeth as a person drunk with the idea of success, and then becomes the robe that Macbeth has dressed himself in that has become pale and weak.
Banquo might be making a joke to amuse his son to state how dark it is: Heaven is trying to be economical ("there's husbandry") with their lights (candles). This also contains an interesting idea--that the lights in the sky are all candles used by the inhabitants of heaven to light their homes.
Macbeth uses an extended metaphor to show his cautious appraisal of the murderers and to fully gauge the kind of men they are. His comparison of men and dogs reveals his belief that men, like dogs, are not created equally and have very different attributes.
Macbeth bitterly states that even though he is king, the witches have given him a "fruitless crown" and an "barren sceptre." Both of these phrases are metaphors for Macbeth's inability to produce children to be his heirs, represent his feelings of inadequacy, and demonstrate why Macbeth fears Banquo and Banquo's children.
That is, dangerous and threatening thoughts plague Macbeth's mind and the fact that Banquo and Fleance live is a constant reminder of the witches' prophesy.
Lady Macduff's son jokingly answers her question with a simile which his mother then continues this idea of her son as a bird with an extended metaphor. His response of "With what I get, I mean; and so do they" means that he will get by however he can. Their witty repartee reveals a fond and loving relationship and makes the end of the scene all the more tragic.
Caithness uses this metaphor to describe Macbeth losing control of his forces. "Buckle" here refers to the rule or control he has over his party, and since he cannot buckle his metaphorical belt, he cannot possible rule over his discontented army.
Bear-baiting was an Elizabethan "sport" or pastime in which a bear was tied to a stake and harassed by dogs. Macbeth uses this metaphor to describe his own condition: he finds it impossible to escape from the superior number of enemies and compares himself to the baited bear. Despite this, he continues to fight against all odds, holding faith in the witches' other prophesy that said no man born of woman may harm Macbeth.