One of the central contradictions the apparitions tell Macbeth in Shakespeare's Macbeth deals with Macduff.
On the one hand, an apparition tells Macbeth to "Beware Macduff." On the other hand, Macbeth is told that he cannot be harmed by anyone born of woman, and that he cannot be vanquished until Birnam Wood comes against his castle at Dunsinane. These are definitely contradictions and mixed messages.
This highlights the fact that Macbeth has a choice in his fate--at least that's one way of interpreting it. Macbeth chooses to believe what he wants to believe. Even though he decides to act against Macduff, he chooses to put his confidence in the witches and believe in his invincibility.
Also, Macbeth is told only to beware Macduff, not to order the slaughter of his family. This almost certainly contributes to desertion on the part of Macbeth's thanes and soldiers, as well as to his wife's mental illness. Once again (as he does in Act I when the witches tell him only that he will be king, not that he will be king immediately by assassinating Duncan), Macbeth chooses to apply heinous action to a rather generic statement or statements.
The witches, therefore, "play" Macbeth. They fool him into over confidence while at the same time steering him into a terrible act that brings about still more destruction to the kingdom of Scotland.