Act II of Macbeth is all about the murder of Duncan. There is talk of the witches; there is obvious treachery; the natural order is distorted; things are definitely not what they seem and over all the battle between good and evil rages on.
Macbeth's ambition and that of Lady Macbeth drive all these forces due to their obsession with power. It is therefore ambition that is prevalent in this particular act and to a lesser extent the effects of guilt.
it does not require much for Macbeth to embrace the weird sisters' vision of him as the ruler of all Scotland.
After Duncan's murder, before he has had time to contemplate his future, Macbeth begins to feel guilt:
Here's the smell of the blood still
He does hear a 'voice ' commanding him to
sleep no more
and he is troubled by feelings of guilt
Wake Duncan with thy knocking! I would thou/ couldst!
However, rather than withdrawing, he is driven to commit more murders to ease the feelings and give him more strength after his initial overwhelming remorse.
There is a significant change in his relationship with his wife. Previously, he was unable to achieve without her encouragement - even to the point of apparent cowardice - whereas as this act progresses he becomes increasingly more independent and will begin to act alone as his personal gratification and his own ambitious vision become more real to him.
The murders have a different effect on Lady Macbeth which is only evident later. At this point, she is still working towards a common goal and feeding her ambitious nature:
wash this filthy witness from your hand
At this point,Macbeth still relies heavily on her vision of their future and his ambition is only vivid whilst she drives him.
Lady Macbeth returns the daggers and stains her hands with Duncan’s blood.
Duncan's sons recognize that someone with overriding ambition was prepared to take it so far as to actually kill the king and know that they are not safe.
This murderous shaft that’s shot/Hath not yet lighted, and our safest way/Is to avoid the aim.
Their decision to leave unfortunately gives Macbeth the opportunity to lay blame at their instance.
Significantly, Macbeth, rather than attend the funeral, goes to his castle to be crowned. The body of Duncan still haunts him but the reader cannot be certain whether this is because he is overwhelmed by what he did or afraid that his committment to his purpose will be compromised.