Why are the witches significant in this play?

In Macbeth, the witches were significant in making macbeths decision to take the throne of Scotland from Duncan. Macbeth had an idea to meet up with the witches but once they told their idea it was confirmed in his mind. Once Macbeth told his wife about the prophecy, she becomes eager to help Without the meeting with the witches, Macbeth probably would not have had the strength to murder Duncan. The entire shape of the story would be different if the witches were excluded.