Through Macbeth's search for power, he must choose between what is morally right or his inner motives. Macbeth gains power over others through the murders of King Duncan, Banquo, and Macduff's entire family along with his servants. After each murder, Macbeth becomes more confident in his search to gain power.
Macbeth's downfall was caused by the deception and temptation of the witches and their prophecies, Lady Macbeth's greed and aspirations for her husband to be king, and Macbeth's own greed, jealousy and ambition. The witches played a colossal role in Macbeth's downfall and ultimately, his death.
What does Macbeth learn from the images of the eight kings? He learns that Banquo's descendants will reign.