Supernatural is defined as of or relating to existence outside the natural world. The supernatural plays a very large and important role in Shakespeare's "Macbeth". Without the supernatural's presence in the play, it would not be nearly as interesting or appealing to the reader. The supernatural is as an important a character in the play as even the title character himself.
In my opinion, the supernatural, including the witches, visions, and the ghost, was as an important and valuable a character to the quality of the plot as Macbeth himself. The three witches, who make their first appearance at the beginning of the play, are the most important and influential aspect of the supernatural in the play. The witches act as a psychic to Macbeth and predict prophecies that will come to him later in the play. The witches also serve to foreshadow events that will take place further into the play and give the reader an idea of what is to come.
The first prophecy from the witches is that there will be a winner and a loser in every battle and Macbeth will be the victor in the battle. Next, the witches refer to Macbeth as the Thane of Cawdor; this is startling to Macbeth as he is currently the Thane of Glamis. .
Macbeth is given the title of Thane of Cawdor later that day because of his heroic actions in battle. The next prophecy the witches give to Macbeth is the one that plants the seed that effectively leads to the downfall of the battle tested warrior, the statement that he will one day become king.
In the play, preceding the murder or King Duncan, Macbeth has a vision of a bloody dagger in the front of him just out of his reach. This vision comes to Macbeth just as he is contemplating whether to go through with his wife's plan of killing the King or to follow his conscience and to spare his friend's life. The bloody dagger seems to push Macbeth over the edge and convinces him to go through with the regicide and gain his throne, following the witches' prophecy.