Clothing imagery in Macbeth furthers the theme of "nothing is/But what is not." For, in Shakespeare's play there are ghosts, hallucinations, deception, and disguise. In Act I, Scene 3, he clothing imagery contributes to the disguise motif as there are garments bestowed upon Macbeth which are an "undeserved dignity."
Ironically, Macbeth asks Ross, "why do you dress me/In borrowed robes?" when bestowed the robe of the traitor, the previous Thane of Cawdor. These robes are, perhaps, the only ones that he truly deserves. both for his bravery in battle against Macdonalwald and for his future traitorous acts. After this award of robes, Macbeth begins to give credibility in the witches' prophesies since they have called him "Thane of Cawdor." He considers now,
If chance will have me King, why chance may crown me.
But, Banquo is suspicious as he notes that the new honors that come to Macbeth do not befit him--"cleave not to their mold/But with the aid of use." They are honors that sit ill with Macbeth; he must dissemble as he wears them. For when he is crowned, Macbeth is not called "king" as was Duncan; instead, he is alluded to as "tyrant."
Indeed, the clothes do not "make the man" as the old adage goes since Macbeth diguises himself in the robes, and the robes do not become him.