In Act IV Scene I, the newly crowned Macbeth returns to the witches for a second visit for clarification on their previous statements. He asks the three witches again for information about what his future holds.
The witches produce three visions and leave it up to Macbeth to determine what they mean.
The first vision is an armed head. The head tells him to beware the Thane of Fife. Remember that the Thane of Fife is MacDuff, whom Macbeth has already been suspicious of, so the vision only confirms his suspicions. The second vision is a bloody child. The vision tells him:
Be bloody, bold, and resolute; laugh to
The power of man, for none of woman born
Shall harm Macbeth.
This makes Macbeth feel confident that anyone who was born from a woman, as most people would be, can't hurt him, so he has no reason to be afraid of them. However, he decides, just to be sure he will kill MacDuff.
The third vision tell Macbeth
Great Birnam Wood is a forest and Dunsinane Hill is where the castle is. This apparition is telling Macbeth that his reign as king will last until the forest comes to the castle. Macbeth can't imagine that the forest can move, so he again feels confident that his rule will be long.
Before leaving the witches have one last message for Macbeth.
Show his eyes, and grieve his heart;
Come like shadows, so depart!
Here they show him a line of 8 kings. The last king is Banquo who is holding a mirror. This shows Macbeth that even though he has killed Banquo, his son (Fleance) lives and will still have sons who will one day be king of Scotland.
These apparitions make Macbeth confident that he controls his future. They are also what cause him to be too confident and will lead to his downfall.