‘The raven himself is hoarse / That croaks the fatal entrance of Duncan’ (Macbeth) so begins Lady Macbeth’s first great soliloquy. The speech comes in Act 1 Scene 5, immediately after Lady Macbeth has received news from a messenger that Duncan, the King, will be arriving at the castle that night, accompanied by Lady Macbeth’s own husband, Macbeth, who has just been made Thane of Cawdor by Duncan. Ravens are often heralds of misfortune or even death: they are ill omens, and Macbeth is a play full of strange omens.
Note that ‘Come, you spirits’ completes the line of blank verse begun by ‘Under my battlements.’ But the line of verse is missing a syllable; the pause between ‘battlements’ and ‘Come’ gives the actor playing Lady Macbeth a chance to take a deep breath before commencing a long invocation. And what an invocation! The ‘mortal thoughts’ which these spirits ‘tend on’ are deadly thoughts: i.e. thoughts of murder. Lady Macbeth’s command that these spirits ‘unsex’ here seems to be a request for her femininity or womanhood to be drained out of her, so she is more ‘manly’ and ready to kill. She wishes to be filled instead with ‘direst cruelty’ from head to toe.
Lady Macbeth wants her blood to be made thick so pity cannot flow through her veins and reach her heart, thus reawakening her sympathy and weakening her murderous resolve. The rest of this section of her speech develop this point: she doesn’t want ‘remorse’ (here used in the more general sense to denote compassion) to be flowing freely through her because her ‘fell [i.e. evil] purpose’ would be shaken by such compunction, or pricking of conscience. The final image (‘nor keep peace between / The effect and it!’) summons the idea of a peacemaker trying to calm down two opposing forces: i.e. her resolve (to murder Duncan) and her conscience and its effects (that will try to persuade her against killing him).
Notice how ‘thick’, formerly applied to Lady Macbeth’s blood, now refers to the night: it’s as if those spirits are already rushing through the darkness to attend on her, and having thickened the air they will go to work on her blood. (This idea of ‘thick night’ will be echoed by Macbeth’s famous line, ‘Light thickens’, later in the play.) This idea of night being ‘thick’ then informs the rest of Lady Macbeth’s speech, which builds on the idea of those spirits being ‘sightless’ or unseen. The word ‘pall’ foreshadows the ‘blanket of the dark’ two lines later: both were probably suggested by the stage on which Macbeth was first performed (the stage was hung with black drapes when a tragedy was performed), but of course, ‘blanket of the dark’ also suggests the idea of night covering the world at night. ‘Pall’, meanwhile, summons death, as in a funeral pall.
The word ‘dunnest’ refers to the dun colour, a sort of dull greyish-brown. Lady Macbeth wants the smoke from hell to rise up to her on earth and shroud her hand as she takes the knife and kills Duncan; she fears that, if she could see what she was doing as she plunged the dagger home, her conscience would cry out for her to leave off (‘Hold, hold!’). This detail is, of course, significant: ‘my keen knife’ tells us that Lady Macbeth initially planned to carry out the deed herself, until she persuades her husband to do it instead.
