What does this quote mean-all hail Macbeth to thee thane of Cawdor?

This quote is from the play "Macbeth" by William Shakespeare. In this scene, Macbeth has just met three witches who have prophesied that he will become king. The quote is spoken by one of the witches, and it means that they are saluting Macbeth as the thane of Cawdor. This is significant because Macbeth is not yet the thane of Cawdor, and the witches' prophecy suggests that he will soon be promoted.