“Lesser than Macbeth, and greater, Not so happy, yet much happier.”
“Stay, you imperfect speakers. Tell me more […] Say from whence you owe this strange intelligence..”
“To win us to our harm, The instruments of darkness tell us truths,Win us with honest trifles, to betray’s in deepest consequence.”
The witches prove their ability to prophesise with the oxymorons – are the witches truly powerful or are their predictions self-fulfilling prophecies? The “instruments of darkness” is advice that Banquo is offering Macbeth about their malevolent nature – he can see the truth, but Macbeth is blinded.
Macbeth finds his voice and commands the witches through imperatives. He demands answers, but in response they vanish – showing the audience Macbeth holds no power over them. Ironically, Banquo here foreshadows future evens as they “betray” Macbeth despite offering some “truth” in their prophesises.