Final answer:
King Duncan awards Macbeth with the title of Thane of Cawdor to honor his successes in battle and his loyalty to the kingdom.
Step-by-step explanation:
King Duncan decides to give Macbeth the title of Thane of Cawdor as a reward for Macbeth's valor and success in suppressing a rebellion and the betrayal by the previous Thane of Cawdor. Appreciative of Macbeth's loyal service and impressed by his bravery in battle, Duncan wishes to honor Macbeth by granting him this title, thus displaying Duncan's belief in rewarding those who have shown deserving loyalty and heroism. The title is an indication of high esteem and trust, as it comes from the king himself, which was a significant honor during that time.