First, the king's praise fills Macbeth with ambition and desire for power. He begins to entertain the thought of becoming king himself, and this ambition eventually drives him to murder Duncan and take the throne.
Second, the king's praise of Lady Macbeth leads her to become more involved in Macbeth's plans. She encourages him to kill Duncan and helps him to carry out the murder.
Third, the king's praise creates a sense of guilt and shame in Macbeth and Lady Macbeth. They feel guilty about killing Duncan and begin to experience hallucinations and other psychological problems. These problems eventually lead to their downfall.
In conclusion, the king's praise of Macbeth and Lady Macbeth has a significant impact on their lives and leads to their eventual downfall.