How does Macbeth interpret the prophecies by the three apparitions?

The witches hail him as "Thane of Glamis" (his present title), "Thane of Cawdor" (the title he will soon receive officially), and "king hereafter" (46-48). Their greeting startles and seems to frighten Macbeth. When Banquo questions the witches as to who they are, they greet him with the phrases "Lesser than Macbeth and greater," "Not so happy, yet much happier," and a man who "shall get kings, though [he] be none" (63-65).

When Macbeth questions them further, the witches vanish into thin air. Almost as soon as they disappear, Ross and Angus appear with the news that the king has granted Macbeth the title of Thane of Cawdor. Macbeth and Banquo step aside to discuss this news; Banquo is of the opinion that the title of Thane of Cawdor might "enkindle" Macbeth to seek the crown as well (119). Macbeth questions why such happy news causes his "seated heart [to] knock at [his] ribs / Against the use of nature," and his thoughts turn immediately and with terror to murdering the king in order to fulfill the witches' second prophesy (135-36).