Final answer:
Shakespeare creates an image of the dead rising to witness and condemn the murder of King Duncan, contributing to the play's dark atmosphere and the theme of natural order's disruption.
Step-by-step explanation:
When Macduff says: "...as from your graves rise up, and walk like spirits to countenance this horror", Shakespeare aims to create a vivid image of the dead rising to witness the atrocity that has unfolded, which is the murder of King Duncan in the play 'Macbeth'.
This invocation of the dead accentuates the unnatural and horrendous nature of the act, indicating that even those at peace in the grave would be disturbed enough to rise and condemn the horror. Macduff's words contribute to the dark and ominous atmosphere of the play and reflect the theme of the natural order being disrupted by the treacherous deeds of Macbeth.