To understand the function of this part of the text we need to look at the scene in context. The witches are preparing for the arrival of Macbeth and the further acts of witchery and deception that they are to practice on him, thanks to Hecate's commands. Thus the purpose of this scene, where the witches prepare the spell in the cauldron, is to deliberately prepare the minds of the audience for the arrival of Macbeth. The list of strange ingredients, ranging from "liver of blaspheming Jew" to "finger of birth-strangled babe" clearly symbolises the evil of the witches, but note how the evil of the ingredients and the witches themselves finds a suitable parallel in the character of Macbeth and the deeds that he has committed and the way that he has given himself over to the forces of evil. Thus, in a sense, the evil symbolism of the ingredients foreshadows the arrival of Macbeth: a man who has relinquished any lingering sense of good to the all-consuming power of darkness within him.