How do the apparitions in Macbeth promote an evil and mysterious mood that contributes to the plot?

Throughout the text there is a continuous reference to the supernatural forces at play in encouraging Macbeth's evil deeds.  In every act of the play there is a substantial reference to witchcraft which in turn establishes a ominous and suspenseful mood for the reader.  Early in the play, the witches themselves serve to create a sense of mystery and suspense as they appear out of nowhere and set Macbeth on a path towards darkness with...

Throughout the text there is a continuous reference to the supernatural forces at play in encouraging Macbeth's evil deeds.  In every act of the play there is a substantial reference to witchcraft which in turn establishes a ominous and suspenseful mood for the reader.  Early in the play, the witches themselves serve to create a sense of mystery and suspense as they appear out of nowhere and set Macbeth on a path towards darkness with their prophecy.  As the play unfolds, Lady Macbeth calls on spirits to make her evil enough to commit the act of murder and then furthers Macbeth's plotting to murder Duncan with her own manipulation of Macbeth.  When Macbeth finally succumbs to Lady Macbeth and the visions of glory imposed by the witches, he gives the famous dagger speech where he invokes the goddess of witchcraft and hallucinates a bloody dagger.  During this speech, Macbeth is consumed by thoughts of apparitions and the tortured dreams of the night disrupting "curtained sleep."  This again sets an ominous mood for the reader as Macbeth moves forward with his plan to murder Duncan.  This mood is continued throughout the rest of the play as the gatekeeper of Iverness (Macbeth's castle) is portrayed as the gatekeeper at the doors of hell and as the witches re-emerge later in the play.  All of these references to the supernatural serve to create suspense within the play and call into question Macbeth's true control over his part in the evil deed of killing Duncan (and many others).