Consider the description of Edward, the English king, in line 146-159 of Act 4, scene 3 of Macbeth. Why is this passage included in the play?

In Act 4, scene 3 of Macbeth, a Doctor briefly enters to tell Malcolm something regarding King Edward:

DOCTOR: There are a crew of wretched souls / That stay his cure. Their malady convinces / The great assay of art, but at his touch - / Such sanctity hath heaven given his hand - / They presently amend. (142-147)

It is an odd passage and it initially feels irrelevant. However, it is important for two reasons. First, the description of King Edward is drastically different from the impression Malcolm and Macduff give of Macbeth. King Edward is deemed a saintly and generous king. He is described as being blessed by God. Macbeth, however, is consistently described as being evil. King Edward is represented as a foil to Macbeth.

Secondly, this passage is placed in the play as an homage to the king. Shakespeare often described the leaders of England reverently, as they were typically patrons of his plays. This description of King Edward is, without a doubt, meant as a compliment to the king.