How does Act 1, Scene 6 contribute to the "fair is foul" theme in Macbeth?

King Duncan has invited himself to dinner at Macbeth's
castle at Inverness. As he approaches the castle, he notes how beautiful it is
there:

This
castle hath a pleasant seat; the air

Nimbly and sweetly
recommends itself

Unto our gentle
senses.

Banquo agrees and
adds his own observations about how peaceful and sweet the castle and the surroundings
seem. Then Lady Macbeth prances down to greet them with fair and loving
words:

All
our service

In every point twice done, and then done
double,

Were poor and single business to
contend

Against those honors deep and broad
wherewith

Your Majesty loads our house. For those of
old,

And the late dignities heap'd up to
them,

We rest your
hermits.

What could be more
hopeful, more loving and more fair: a beautiful place and a lovely hostess. Fair, fair
fair.

Yet, within mere hours, this delicately sweet
environment will be turned in a place of unnatural, bloody murder by the very woman who
greets the king so sweetly and by her equally gracious husband and duplicitous. Foul,
foul foul.

So, what seemed so fair to the innocent senses
of an old and kindly king, will soon be turned into the putrid jaws of hell. Fair is
foul, and foul is fair... indeed.