Final answer:
The line 'Glamis, thou art, and Cawdor; and shalt be' is from Shakespeare's play Macbeth. It is spoken by the witches and foreshadows Macbeth's future as Thane of Glamis and Thane of Cawdor, as well as his eventual rise to the kingship.
Step-by-step explanation:
The line 'Glamis, thou art, and Cawdor; and shalt be' is from Shakespeare's play Macbeth. This line is spoken by the witches in Act I, Scene 3, and it serves to foreshadow Macbeth's future as the Thane of Glamis and the Thane of Cawdor, and also his eventual rise to the kingship. The line suggests that Macbeth will fulfill these prophecies, but it also hints at his internal struggle with ambition and moral hesitation due to his 'milk of human kindness'.