In Macbeth, what does Banquo mean when he says the following quote?"Thou hast it now: King, Cawdor, Glamis, all, As the Weird Women promis'd; and I...

This famous quote opens Act III, and it is important to
realise how vital this quote is. Banquo has silently witnessed what has transpired in
Act II and how Duncan has been assassinated and Macbeth has seized power. He alone was
there with Macbeth when the witches predicted that Macbeth would become Thane of Cawdor,
Glamis, and then King, and now we see that he suspects Macbeth of having gained these
prophesied titled through foul means, as Banquo says tha the fears that Macbeth
"play'dst most foully" for the titles he has won. This is a very important soliloquy in
the play therefore, as in it Banquo voices the suspicions that he has of Macbeth and
internally debates the truth of the prophecies of the "Weird Women." For Banquo, too,
received prophecies, and surely if the prophecies that applied to Macbeth came true,
then those relevant to Banquo will come true as well. However, as that involved one of
Banquo's heirs becoming King, this is potentially a treacherous thought, so he is quick
to be silent when he hears other characters enter.