The witches amplify the theme of deception and equivocation within Act 4.
Act 4 begins with the witches speaking in proverbial (common) supernatural phrases) such as "eye of a newt" and "cauldron bubble".
This conforms to the archetype (norm) of witches that the audience would fear.
The Jacobean audience believed that there was a 'Macbeth' curse and that their spells could breakthrough in the play, therefore this was petrifying for the audience.
The allusions to heat and hell epitomise their evil nature. ("fire" and "burn")
The witches summon three apparitions which are manifestations of the threats Macbeth faces:
"an armedhead" warns Macbeth of Macduff, it is emblematic (symbolic) of the violence of battle and foreshadows Macbeth's decapitation.
The witches summon three apparitions which are manifestations of the threats Macbeth faces:
A "bloodychild" serves to represent Macduff who was born by Caesarean section.
The witches summon three apparitions which are manifestations of the threats Macbeth faces:
A "child crowned with a tree on his head" which could represent the rightful heir to the throne, Malcom.
The tree could be emblematic of Birnam wood, where Macbeth lives or the natural imagery could suggest that Scotland would flourish under Malcom's rule.
Each of the prophecies are equivocal (vague).
The second part is pertinent (important) in revealing "none of woman born shall harm Macbeth" which is ambiguous.
Macbeth's hubris denies him from being able to read into their deception.