(aside) The prince of Cumberland! That is a step
On which I must fall down, or else o’erleap,
For in my way it lies. Stars, hide your fires;
Let not light see my black and deep desires.
The eye wink at the hand, yet let that be
Which the eye fears, when it is done, to see.

Macbeth is saying that Malcom will be a prince of Cumberland. To be a king I have to go up to him or I give up. Macbeth wants the star to hide the light.