This film version is markedly different from the play in a number of ways. For example, all of the Porter’s racy lines had to be cut, censorship being extremely strict in the 1940s. Moreover, the character of Donalbain is removed altogether and various lines were edited or reassigned.
Welles even chose to add a character, the Holy Man, whose purpose, according to the director and star, was to portray the battle between the ‘old’ religion (Paganism, which is represented by the witches) and ‘new’ religion (Christianity).
The witches in the 1948 version of Macbeth had a much
more active role in the tragic hero's downfallHowever, significant changes can also be found in the witches, who have a much more prominent role in the film than the one they have in the play, Welles’ witches even make an appearance after the death of Macbeth.
The implication seems to be that their part in the downfall of Macbeth is much more active than it might appear in Shakespeare’s version.