Macbeth sees the final apparition after seeing three apparitions that frankly make him feel very confident. He feels indestructable when the apparition notes that no one of woman birth can harm him and it won't be until the woods come to the castle that he die. It seems as though Macbeth may be immortal!
However, this final apparition plays on Macbeth's biggest fear, that he will have no children succeed him as king. Remember, the witches told Banquo that Banquo's kids will be king. Well, here the apparition shows ghostly figure after ghostly figure that all resemble Banquo. Each of these men hold scepters or royal staffs indicating their place on a throne. Finally at the end of this line, Banquo appears, bloodied, smiling, and mocking Macbeth. Although Macbeth had Banquo killed, Banquo still gets what Macbeth was trying to prevent, a long line of royalty.
Throughout the announcement of what he visually sees, he begs the "filthy hags" or the witches to explain what is going on. This tone he takes with them shows his fear.