What is the meaning of 'The Thane of Cawdor lives Why do you dress me In borrowed robes' in 'Macbeth'?

In response to his being greeted with another's title instead of his own as General and Thane of Glamis, Macbeth asks, "The Thane of Cawdor lives. Why do you dress me/In borrowed robes?"

Specifically, the question is in Act 1 Scene 3 of the Shakespearean play. The noble Scotsmen Angus and Ross seek out friends and fellow Generals Macbeth (c. 1014-August 15, 1057) and Banquo. They hail Macbeth as Thane of Cawdor.

Macbeth already is Thane of Glamis. As far as he knows, the powerful Cawdor title and possessions still are held by another noble Scotsman. He does not know that Cawdor has been arrested for treason and undoubtedly tortured into confessing his guilt and unworthiness to live.

The disposition of the Cawdor title and possessions therefore is up to King Duncan I (d. August 14, 1040). The King may not be one to share, and Macbeth therefore may find it surprising for someone other than the King's son to receive anything other than passing gratitude. For example, the King honors Banquo with a mere "thanks" for saving Scotland from invading Norwegians and rebellious Scotsmen.