What is the importance of the opening act/scene of Macbeth?

In the opening scene of Macbeth, the witches are
discussing a meeting that they plan to have with Macbeth. This scene sets the tone which
is filled with suspense. The reader is interested in the witches' actions. There is an
element of suspense. The reader becomes intrigued by what the witches are
discussing.

With this opening scene, the reader is curious
about what the witches plan to share with Macbeth. The witches' conversation fascinates
the reader:

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Fair is foul, and foul is fair.
Hover
through the fog and filthy
air.

This statement creates a
sense of danger. What could be so important? What do the witches desire to share with
Macbeth? Macbeth is a busy man. He is on the battlefield, yet these witches plan to
enlighten Macbeth. The opening scene sets the stage for dread and foreboding evil. These
witches are up to no good. They have a plan that will change Macbeth's life forever.