Act 4, scene 3: Why might Shakespeare have included the scene regarding the king (lines 159-181)?

People during Shakespeare's time believed that kings had a divine right to rule and that they were a step closer to God than regular, non-royal people. Therefore, it was more than murder to kill a king: it was regicide—a crime against country and God. If a person intends to depose a king, and to kill that king, they must grapple with the issue of divine right. What gives one king the right to kill another? Aren't they equals in the eyes of God?
This scene, where Malcolm, a doctor, and Macduff discuss the healing powers possessed by the king of England, firmly establishes that king's superiority over Macbeth, as Macbeth has no such divine powers. The king of England has the power to heal the sick with "his touch" and can cure them of a terrible and deadly disease simply by laying his hands on them (4.3.163). This provides evidence that this king is closer to God and is truly divine, as he does something that Jesus could do, while Macbeth cannot. This information, in a way, skirts the issue of divine right and allows those who rise against Macbeth to claim the moral high ground.