Macbeth opens with the witches and the audience knows that what will follow will be dramatic and unexpected, in keeping with the witches mantra that "fair is foul and foul is fair." (I.i.10) Even Macbeth's first appearance is on the battlefield and his connection to the witches is established as "so foul and fair a day I have not seen."(I.iii.38)
Macbeth is set in Scotland and much of the drama takes place in the dark, whether it is under threat of a thunderstorm or in a castle. The darkness establishes Macbeth's own mood and creates a sense of foreboding. The scene is then set for chaos and evil. Macbeth, the audience knows, is very affected by circumstance and opportunity and his "vaulting ambition" will ultimately be satisfied as his belief in the witches prophesies and his own invincibility combine to cause Macbeth's final ruin.
The initial setting which reinforces the mystery surrounding the witches and the possible consequences if Macbeth "shalt be King hereafter"(I.iii.50) encourages Macbeth's delusions of grandeur. His confusion, but at the same time excitement at his improved prospects , enhances the tension created by this setting and, although he knows it "cannot be ill; cannot be good,"(131) it gives him "earnest of success."(132)
Later, when his castle is the setting, Macbeth, with Lady Macbeth's constant aggression - masquerading as encouragement - succumbs to evil forces as "the bell invites me."(II.i.62) After he has killed Duncan, he is so affected by his surroundings that he can barely stop himself and continues his murderous activities, killing Duncan's servants and, even outside Lady Macbeth's knowledge, Banquo.
In order to continue, Macbeth needs some confirmation and again seeks out the witches in (a dark cave, a cauldron boiling) which sets the scene at the beginning of Act four, revealing that Macbeth is far from finished establishing his future. Macbeth becomes more tense the more he hears and demands to "be satisfied" (IV.i.103) failing which he promises "an eternal curse fall upon you." (105) He is even challenging the witches now, so overwhelmed by his surroundings.
Macbeth is already a confident soldier but knowing that he cannot be defeated "until Great Birnam Wood....shall come against him" (93) and no man "of woman born"(80) can harm him, Macbeth fails to recognize that these forces are conspiring to create a tension that he is barely able to restrain. The environment is one he is so comfortable in, a battlefield and he will realise too late that the witches are nothing more than "juggling fiends."(V.viii.19)