When King Duncan realizes that he was betrayed by the past Thane of Cawdor, he says,
“There’s no art to find the mind’s construction in the face:
He was a gentleman on whom I built an absolute trust.”
This means that Duncan used to trust the Thane of Cawdor with his eyes closed but then Ross reveals to Duncan that the Thane of Cawdor betrayed him by joining hands with Duncan’s enemy, the king of Norway. Ross describes this deed as,
“Norway himself, with terrible numbers, assisted by that most disloyal traitor,
The Thane of Cawdor, began a dismal conflict.”
Due to this betrayal, the Thane of Cawdor is executed, so Duncan chooses Macbeth to receive this title. Duncan chooses Macbeth because he is fearless in battle, especially against the Norwegians when he ploughed through the ranks of soldiers to kill Macdonwald.
King Duncan publicly compliments Macbeth when saying,
“O worthiest cousin! The sin of my ingratitude even now was heavy on me: thou art so far before that swiftest wing of recompense is slow to overtake thee. Would thou hadst less deserved, that the proportion both of thanks and payment Might have been mine! Only I have left to say, more is thy due than more than all can pay.”
He means that he is grateful to Macbeth for playing a major part in the victory that they had had earlier and that he can think of nothing to repay him enough. This shows the respect that Duncan had for Macbeth.
Duncan thinks that he can trust Macbeth. Duncan also makes Malcolm the Prince of Cumberland. In Act 1 Scene 3, Macbeth and Banquo meet the witches and they predict that Macbeth will become king, “All hail Macbeth that shall be king hereafter.”
Macbeth is happy to hear this