Shakespeare's Holy Grail:

At first, Macbeth is too ‘full of the milk of human kindness’ to contemplate murdering the king. But she browbeats, mocks, humiliates and manipulates him till he agrees to the murder. They, just as did Adam and Eve, both have now ‘fallen’ into the duality of good-and-evil.

Duncan, on the other hand, is described as no ordinary king, but a deity. He represents the very soul of man, the breath of God, the source of life that feeds the soul of all mankind. When Macduff discovers the murder, whose loss could possibly evoke such an inconsolable wailing? A mere mortal king? No chance. The loss of the life within the Lord’s anointed Temple (the soul)? Absolutely.

 O horror, horror, horror,

tongue nor heart cannot conceive or name thee…

…Confusion now hath made his masterpiece:

most sacrilegious murther

hath broke ope

The Lord’s anointed Temple

and stole thence

The life of the building.

Macbeth, Act II Scene III

It is indeed a dangerous, daring slice of heresy to suggest the body (not the church building) is the anointed temple of the Christ — even today.

When he kills Duncan, Macbeth finds he has banished his very soul, bringing darkness and despair to the whole of Scotland. Scotland here represents the consciousness of mankind, just as in Hamlet it is Denmark and in King Lear it is ancient Britain. Order is lost; something is rotten.

Here Macbeth has become as Cain, the son of Perdition. Scotland, the whole world of our consciousness, is now shrouded in darkness and stained with Macbeth’s shame. Macbeth has given ‘the eternal jewel to the common enemy of man’. The crown he stole has become hollow, fruitless and worthless. But having lost his soul, like Cain, he cannot stop himself from compulsively murdering anyone who might threaten his empty throne. Even his almost-brother Banquo.