Act 4: these witches sound more plausible than Hecate, but then Hecate returns for a moment. The apparitions that follow set up the ironies that will conclude, the bloody child as a baby fresh from Caesarian delivery, the crowned child with a tree, foreshadowing the movement of Birnam Wood. (It’s rather weird that Santa Barbara and Montecito have a golf course by that name at their border; it must have sounded suitably Scottish and right for golf, and no Shakespeareans were around to raise questions.) In the line of eight kings, Banquo is still bloody, “blood-boltered.” Presumably the last one with a mirror reflected King James, who became the ninth? Is this how you understand this? The “antic round” for “this great king” must be a celebration of James, paying welcome to him to the English throne. Macbeth says in his aside that in the future the firstlings of his heart will be the firstlings of his hand: no more overthinking things. First to Macduff’s castle to kill his family.
Then to this very scene, 4.2, where we see the consequence of Macduff’s flight. The son is one of those precocious Shakespearean children. The messenger provides the narrative, and the murderer acts quickly. Macbeth has become the Herod of mystery plays.
Malcolm’s initial deception of Macduff and then his revelation of his actual character seem rather elaborate, but serve to show the necessity of character in a ruler. And this leads to the showing of the “king’s evil,” which I think was practiced by James. Ross brings Macduff the news of his family’s deaths, and his reaction. “He has no children” seems to refer to Malcolm in the immediate circumstance, but it could reflect onto Macbeth as well. But Macduff’s “But I must first feel it as a man” clearly addresses the theme of manhood which Lady M had introduced and the murders of Banquo had expressed.
I take your point that Shakespeare is interested in exploring the origin of evil: where does it come from? Yes, at the outset Macbeth is ambitious but still innocent, though even before meeting the witches in 1.1. he presumably entertains thoughts of being king, and dark thoughts about how that might happen (Duncan would have to die). It put me in mind of Paradise Lost, where Adam explains Eve’s evil dream in Bk. 4: “evil may come into the mind of god or man/ May come or go, so unapproved, and leave/ No spot or blame behind.” So until Macbeth “approves” evil, decides to proceed, he is innocent. But Macbeth is unlike Eve, who is tested, reassured, then tempted in Bk. 9 by Satan, and after a long discussion about whether or not to proceed, goes ahead (having convinced herself that eating is OK.) Macbeth resists evil thoughts, decides against them, but then he pretty quickly “falls,” after a single rousing speech from his wife. As early in the play as 1.7 he has decided to go ahead, even though he knows full well that he will commit evil. We’ve got four more acts, suggesting that Shakespeare is even more interested in exploring how Macbeth deals with the evil act he has committed. More on that later.
If the play really traces Macbeth’s “fall,” from initial innocence to guilt, then you would think Shakespeare would want to establish his innocence more clearly. But it’s pretty clear from as early as 1.1 that he has evil thoughts. By the same token, you might think the mild and delicate air would be described at the beginning of the play, not in the sixth scene. Shakespeare begins the play with “filthy” and “foul” air, and with a warning that what looks “fair” could in fact be “foul.”
As for the “origin” of evil, doesn’t it let Macbeth off the hook if we say that the evil thoughts “come from” the witches, unless the witches are an outward and visible sign of the evil thoughts that constantly circulate through the world and mind of man?
In 3.6 I’m still not sure why Lenox speaks ironically rather than directly.