Although it is certainly true that Macduff is suspicious of Macbeth, there is also another reason that Macduff is so resistant to Macbeth 's kingship throughout the play: his strong belief in the divine right of kings, which was a prevalent belief during Shakespeare's time. Essentially, the divine right...
Although it is certainly true that Macduff is suspicious of Macbeth, there is also another reason that Macduff is so resistant to Macbeth's kingship throughout the play: his strong belief in the divine right of kings, which was a prevalent belief during Shakespeare's time. Essentially, the divine right of kings was a premise that God established the line of kings. Therefore, any interruption in that line would bring chaos and disfavor. Since Macbeth did disrupt the natural line, Macduff, even with no knowledge of his more nefarious part in Duncan's end, views him negatively.
The reader can begin to see chaos happen the very night that Duncan is murdered. The old man in act 2, scene 4 claims,
Even like the deed that’s done. On Tuesday last,
A falcon, tow'ring in her pride of place,
Was by a mousing owl hawked at and killed. (11–14)
The old man's description links the death of the God-appointed king with immediate disruptions in nature. Macbeth's kingship continues to create disorder in the natural world, further asserting the idea that he is not the king whom God desires to rule over Scotland. Macduff mentions this when he speaks with Malcolm, the rightful heir, in act 4, scene 3. Macduff claims that each day in Scotland under Macbeth's rule
New widows howl, new orphans cry, new sorrows
Strike heaven on the face, that it resounds
As if it felt with Scotland and yelled out
Like syllable of dolor. (5–8)
Macduff follows this sad description up with his claim to Malcolm, in response to Malcolm's list of his own faults, that
In nature is a tyranny. It hath been
The untimely emptying of the happy throne And fall of many kings. But fear not yet
To take upon you what is yours. (67–71)
Macduff truly believes that it doesn't matter what Malcolm's weaknesses are; because Malcolm possesses the divine right of kings, he has the responsibility to take up what is his.
Therefore, it wouldn't have mattered on some level who became king after Duncan if it wasn't Malcolm. Macduff represents a large groups of the citizenry who would have seen Macbeth's ascension to the throne as a usurpation and an act of defiance against God's order that is restored, not only with Macbeth's death, but with Malcolm's rightful ascension.