The apparitions in Act 4, scene 1 speak to Macbeth three times.
First Macbeth is told to beware of Macduff. The apparitions also tell Macbeth to be bloody and bold. Then Macbeth is told that he will not be harmed by any born of a woman. Finally, he is told that he will not be vanquished until the Great Birnam wood (forest) is moved to the Dunsinane Hill.
These last two messages seem to suggest that Macbeth will be completely safe from all and any human being, since people, for the most part, are all born from a mother and forests don't move.
Macbeth interprets these messages as they are intended to be interpreted. He takes them as good signs which suggest that he might be invulnerable. He grows confident and immediately makes a plan to attack Macduff and kill his family.