Basically this is Macbeth talking to Lady Macbeth, and he is explaining to her why he killed the guards. There will be more like this.
MACBETH: O yet I do repent me of my fury
That I did kill them. But my Lady,
What appalls thee so?
Thou knowest the sleeping dead are but pictures.
The death of Duncan was of great moment,
But to kill these other two was a trifling toy.
I have done the deed, so why not repeat it?
They are better dead than alive.
The pale hands of these two cowards
Would soon be known incapable of such a sin.
Banquo doth wish for a meeting in which
We could question this bloody piece of work
To know't further. This doth perturb me.
These two fools are a threat to us,
They have all in their power
To deny all accusation made against them.
By dispatching them, therefore slaughtering
All proof of their unmanly innocence,
And I have created an ideal image.
Thus have I dressed the guards as murderers.
There they lie, steeped in the colour of their trade.
Those sparrows which one thought did assalt the owl,
Whilst I, the raven and true culprit, do withdraw
Like an innocent flower, unsuspected, and,
Being the serpent underneath, go wallow
In the beauty of my triumph.