Richard Green Moulton

“ Banquo was a natural rival of Macbeth (3.1. 50-7) . 3. The main function of the supernatural element in a play is to add dramatic force to the working of events. By the interposition of the Witches the 'working of events' takes the form of a 'destiny' which appears
(1) irresistible:
Throughout, obstacles thrown in the way of the 'destiny' become the means by which it is worked out. ”

“ Shakespeare seems to assume for any story he presents whatever was believed in by the age to which the story belongs—but the poet is himself responsible for the interpretation underlying the story, in this case for the use made of the supernatural agency—thus the true 'rationalisation' enquires how the operation of the supernatural element in a play harmonises with reason and morals. ”

“ Effect of the Witches vanishing [1. 3. 78, and compare 4. 1. 133] .
The "honest trifles" principle (1. 3. 122) : prying into forbidden knowledge finds a fitting nemesis in obtaining only half truths.
The gods punish men by granting their prayers. [Macbeth's Vision of King's in 4. 1.; especially note 103.—Compare in 3. 4 apparition of Banquo in response to invitations.] To sum up: Macbeth was the actor in the scene of his destiny: did the Witches do more than turn the (coloured) footlights on it? ”