What are Banquo's concern about the witches' prophecies?What is Macbeth's response?Its from the book Macbeth by Shakespeare

Upon the first meeting with the witches' Banquo seems to
be as fascinated by them as is Macbeth.  After they tell Macbeth that he is to be "king
hereafter," Banquo eagerly wants to know his own fate.  Yet Macbeth's and Banquo's
 responses are quite different.  While Macbeth seems "rapt" with the idea that the
prophecies might in fact come true, Banquo is much more skeptical.  He warns
Macbeth:

And
oftentimes, to win us to our harm,

The instruments of
darkness tell us truths,

Win us with honest trifles, to
betray's

In deepest
consequence.

In other words,
Banquo thinks that the witches may seem to be  telling truths, but they are only telling
part of the truth.  He thinks they may be deceiving them as to the true meaning of their
words.  He calls the witches "instruments of darkness" capable of betraying men with
their words.

Macbeth, though, does not heed this warning.
 His immediate thought is making the third prophesy come true. His faith in the witches
seems to be justified.  They have correctly identified him as Thane of Glamis; their
prediction that he would become Thane of Cawdor has been immediately fulfilled, so it
seems reasonable for Macbeth to conclude that he will become king shortly.  The question
is how will he become king.  Will chance crown him king without his having to do
anything, or will he need to commit a deed that he can at this point only shudder to
think about?

Banquo seems more cautious, more skeptical,
and unwilling to act on the witches' prophecies to him.  It must be noted, however, that
the witches' prophecies for Banquo are much more obscure and more difficult to achieve
immediately.  But Macbeth seems to believe the witches' completely.  He does not doubt
their motives or the truth of their words.  This faith in the witches continues
throughout most of the play and is partially responsible for Macbeth's
downfall