A comparison using like or as is a simile.
When Macbeth is greeted by the weird sisters as Thane of Cawdor and the future king he is speechless. Then, when he learns that he was named Thane of Cawdor, he thinks that the witches have to be right in everything they say, and he starts imagining that he murders King Duncan. That fantasy is less important for him than the things that are not yet true.
