Mack, Maynard Jr. "The Voice in the Sword."
Killing the King: Three Studies in Shakespeare's Tragic Structure. New Haven: Yale UP, 1973. 138-185.

The general task that Mack sets for himself is to explore how ideas about kingship are used as dramatic resources in three of Shakespeare's tragedies, Richard II, Hamlet, and Macbeth.

Mack's starting point is an idea -- and a fact -- about kings that was often expressed in Shakespeare's time by the legal doctrine that the king had "Two Bodies." One was the natural body, which could die, and the other was the body politic, which could not die, so that you still had to pay the king's taxes when the king died. This was not merely a legal doctrine, but also a common idea. For example, in Hamlet it's mentioned that "Norway" is bedridden; the man who is sick is also the king who is Norway.

This idea, Mack says, makes kings good dramatic material for two reasons:

The first is the simple fact that as leader of his people a king occupies a position that makes his experience uniquely important, exemplary, and symbolic, and therefore immediately attractive to the artist, who is a creator of symbols. A complex conception of kingship, therefore, is an ideal vehicle for conveying and exploring complex conceptions of other people and values. The other appealing aspect of twinned kingship is the drama automatically implicit in a twinned but single creature. This use neither supposes that the king is really two different functions nor claims that he is in fact unified. It stresses the tense middle ground bound to exist between the two functions and marks this middle position as the "reality" of kingship.  (2)

Concerning Macbeth, Mack says that the killing of the king was doomed to ultimate failure and destroyed the soul of Macbeth:

The king can be killed, but the whole world, human, natural, and supernatural reacts to offer a new king. Regicide is finally in some strange way impossible, for better and for worse. At a profounder level, what we have seen is the destruction of a soul [Macbeth's], whose intuitions of a life beyond life are his glory and become his ruin; we go from the savageries within a man to the savageries of the battle that cuts him down, from a hero who sees more deeply into the abyss than we do to a villain, who, like his opposers, sees far less. Regicide easily becomes a mysterious sort of suicide, spiritual and physical.  (184-185)
Mack always writes clearly and persuasively, but I found more value in his analyses of image-clusters than in his more general ideas. These analyses provide insight into patterns of both thematic and character development. Here, for example, is a paragraph from his discussion of banqueting:
In the banquet scene this all-pervasive alienation receives clear expression in Macbeth's peculiar situation of being alone in company and in company (the company of his wife and the Ghost) when alone. Any echo here of the regal scene at Forres, such as the chair or chairs of state already mentioned will accentuate yet more the fact that he has brought his isolation from the edge of that scene to the very heart of this one, where (apparently) he never occupies his "state" at all. The scene is pivotal, moreover, in that up to this point we have always seen Macbeth alone against the others, whereas here "the others"--first in the form of the Ghost--begin to engage together against him. Soon, in the persons of Lennox (, a Messenger (IV.ii), Macduff, Siward, and Malcolm (IV.iii), and nearly all of Scotland (V.ii), the balance will shift until all companies and companions are set against the king. Either way he is isolated among crowds, unable to participate at life's feast. The final stage in his spiritual starvation--"I have almost forgot the taste of fears . . . I have supp'd full with horrors" (V.v.9-13)--will recall us to this moment in the banquet scene, and also to that other moment, as he stood withdrawn in his house from another banquet, set for Duncan, when his hunger for power and security his humanity began to starve.  (142)

Bottom Line: Excellent scholarly work.