How do Macbeth's soliloquies position the audience?

If I understand your question, Macbeth's soliloquies help
develop pathos for a character who otherwise we would simply view as a villain.  From
the beginning we are allowed inside Macbeth's mind as he contemplates the image of the
slaughtered Duncan and shudders.  Later we see him agonizing over the ethical reasons
that Duncan should not be killed:  Duncan is a good king, he is Macbeth's kinsman, he is
Macbeth's guest.  Even after he commits the murder of Duncan, Macbeth's soliloquies show
us that this murder has only made Macbeth paranoid, fearful that his ill-gotten gains
may be taken away, and so the unhappy Macbeth plans a further murder.  Throughout the
play, Macbeth's soliloquies show the audience that the murders have not brought Macbeth
any degree of happiness, security, well being.  Instead, they have caused him to lose
his wife, his honor, his friends, the respect of his countrymen.  In one of his most
eloquent soliloquies, Macbeth's reflection shows his
despair:

My
way of life

Is fall'n in to the sere, the  yellow
leaf;

And that which should accompany old
age,

As honour, love, obedience, troops of
friends,

I must not look  to have (Act 5, scene
3)

This keen awareness of the
consequences of his actions, the misery that has resulted, make us understand the
workings of a guilty conscience.  While we do not condone Macbeth's actions in any way,
we do to some extent understand his pain and this understanding makes the audience
somewhat more sympathetic than we would be without the soliloquies.  Don't get me wrong,
Macbeth's actions are horrific, and he should feel pain and remorse.  But the fact is
that many murderers do not feel the agony that Macbeth feels throughout the play. In
this way, we can identify much more easily with Macbeth who succumbs to temptation, digs
himself deeper, and suffers greatly than we can to other villains, such as Iago in
Othello, who feels no such guilty pangs.