Final answer:
Macbeth questions Ross's announcement about being named Thane of Cawdor using the metaphor 'borrow'd robes' to express disbelief and suspicion towards an honor he believes is not rightly his. The metaphor conveys the transient and suspicious nature of unexpected honors and reflects the play's themes of ambition, power, and legitimacy.
Step-by-step explanation:
When Ross informs Macbeth that he has been named Thane of Cawdor, Macbeth is incredulous, saying 'Why do you dress me in borrow'd robes?' Here, dressing in 'borrowed robes' serves as a metaphor for assuming a title that does not rightly belong to oneself or is not permanently held. Macbeth is aware that the current Thane of Cawdor is still alive, therefore, to him it seems strange to be given a title that is already possessed by another man.
The metaphor reflects the surprising and possibly suspicious nature of receiving an honor unexpectedly and underscores Macbeth's disbelief in the witches' prophecy. In this context, the metaphor also suggests the transient and potentially ill-fitting nature of titles and honors, which may not become a part of one's identity as smoothly as tailor-made clothing.
The use of the metaphor hints at the idea of pretense and undeserved status. Macbeth perhaps feels he is being dressed up in honors that he has not earned, which is reflective of the play's broader themes of ambition, power, and legitimacy. This sense of unease aligns with the overall moral ambiguity and the blurred lines between good and evil in Shakespeare's tragedy.