At least according to another of the floating manifestations of some hagg preparing a cauldron. This apparition that foretells the future probably has the most powerful influence on Macbeth than all the other apparitions that come to haunt, warn. and encourage Macbeth because to him it means that until a hill and a forest come against Macbeth, no harm will come to Macbeth. But also that as long as a pair of natural formations do not clash with Macbeth he will not be defeated either, or at least that is how Macbeth interpreted what he was told by the third apparition. Although he doesn't know it, what the third apparition was really saying wasn't that until a pair of landforms called the Great Birnam Wood and the high hill of Dunsinane attacked Macbeth, that would be the time which Macbeth would be defeated. But that Macbeth was about to be defeated when all the people living in the Great Birnam Wood area across the high hill of Dunsinane rose up and fought against him that's when he will finally be defeated, and his kingdom will truly come at the end. END. So Macbeth will get a nasty surprise in the near future when he realizes that he will have a much shorter reign than that