Hecate, the "mistress of the witches," doesn't show up until Act III, scene 5. Like Macbeth, we as an audience have believed the three Weird sisters were frightening and powerful—until Hecate's arrival.

Hecate is very angry that the witches have acted without consulting with her first. She is also angry that they have helped Macbeth. She doesn't think he's worthy of their aid, and she tells them she knows he won't do anything for them in return for their help. She calls him "spiteful and wrathful" and out only for himself. Therefore, she wants the witches to trick him and lead him to his doom.

While all along we have been frightened of the Weird Sisters, we see them cowed and intimidated by Hecate. She scolds them severely saying:

let’s make haste; she’ll soon be back again.

To answer this question, take a look at Act III, Scene V of Macbeth, in which Hecate, the ruler of the witches, gives them explicit instructions about what to do next. Firstly, she tells them that in the morning, they must meet her in the "pit of Acheron." Acheron is a word taken from Greek mythology which means the River of Hades, or hell, as we would call it. She wants the witches to meet her there because she knows that Macbeth will come there to ask more questions about his future.

Secondly, she tells the witches to bring their "charms and everything beside," meaning their spells, cauldrons, and other objects associated with magic.

Hecate gives the witches these instructions because she intends to cast a spell that will produce illusions to trick Macbeth. This creates dramatic irony because we know that Macbeth will be tricked by Hecate, whereas Macbeth does not. He believes everything the witches tell him and has not considered that their prophecies might be works of fiction.

Hecate is indeed angry, for the witches have "trade[d] and traffic[ed]" with Macbeth without including her. She considers him a "wayward son", self-serving and ungrateful. She wants the other witches to "make amends"--that is, to set things right. They are to work with her to set Macbeth up for failure, using his own hubris and his weak humanity against him. Hecate knows that humans, being mortal, crave security; therefore, she wants the witches help her manipulate Macbeth's emotions. She wants him to "spurn fate" and "scorn death", and, ultimately, place his own hopes above "wisdom, grace and fear." Which means she wants them to help her trick him into a false sense of security so that he will then make the fool-hardy mistakes that will bring about his undoing.

Hecate is upset because the other Witches did not consul her before they spoke to Macbeth. Hecate assures them she will conjure a spell that will lead Macbeth to a disastrous fate. She sends them to cast the spell and prepare the charm, as Macbeth plans to visit them soon.