The witches prophecy to Macbeth is straightforward:
"First Witch. All hall, Macbeth! hail to thee,
Thane of Glamis!
Sec. Witch. All hail, Macbeth! hall to thee,
Thane of Cawdor!
Third Witch. All hail, Macbeth! that shalt be
king hereafter." (Shakespeare)
For Banquo, the message is more veiled:
"Third Witch. Thou shalt get kings, though
thou be none:
So, all hail, Macbeth and Banquo!"
When the two of them talk about the prophecy, it is clear that Banquo will be father to kings, and therefore greater than Macbeth.
"Ban. Were such things here as we do speak
Or have we eaten on the insane root
That takes the reason prisoner?
Macb. Your children shall be kings.
Ban. You shall be king." (Shakespeare)
In Macbeth, Macbeth and Banquo receive the original prophecies from the witches in Act 1, Scene 3. During an impromptu meeting, the witches tell Macbeth that he will become the Thane of Cawdor and, later, the King of Scotland. Macbeth is excited by these prophecies: Banquo notices that he seems "rapt," for instance, although he cannot imagine how they will come true.
In contrast, Banquo is told that he will be "lesser than Macbeth" and that instead of becoming a great leader or king himself, it is his descendants who will rise to royal prominence:
"Thou shall get kings, though thou be none."
More importantly, however, Banquo will be much "happier" than Macbeth.
When Macbeth and Banquo ask how the witches have come to know such information, the women simply vanish into thin air. This sudden disappearance further piques the curiosity of Macbeth and Banquo, leaving them to ponder the potential truth of these prophecies.
Macbeth opens with three witches on an open heath in Scotland. A civil war is being fought nearby, and when the battle is won Macbeth and Banquo leave the field of battle and meet up with the witches (which the witches had predicted would happen).
The witches prophesy that Macbeth will become Thane of Cawdor and ultimately will be King. They predict that Banquo will “get” kings – meaning that he will be the father of kings – but he will not be king himself. They also predict that although Banquo will not rise in power in the same way Macbeth will, he will be happier and greater.