The witches effect in Macbeth

The three witches in the tragedy Macbeth are introduced right at the beginning of the play and the brief opening few scenes give an immediate impression of mystery, horror and uncertainty. This is a sign of things to come as witchcraft is used as one of the main themes of the play. The witches create an atmosphere of evil and disorder.
In the opening scene the weather is thunder and lightning which is a mirror image of the way the witches are perceived. When you think of thunder and lightning you think of evil and destruction, this is exactly the way witches are represented in this play. They are evil and cause destruction in Macbeth´s life.

Banquo says in act 1 scene 3 line 124:
"The instruments of darkness tell us truths, Win us with honest trifles, to betray's In deepest consequence."
He thinks and says bad things of the witches. He calls them instruments of darkness and the devil. He believes that these prophecies will only bring harm even before anything begins to happen...