Stars, hide your fires; Let not light see my black and deep desires.
Act 1 Scene 4 lines 52-53
Said by Macbeth at the beginning of the play in Act 1 Scene 4, these words show us the initial hesitations of the character. He discusses his current position with himself: now Macbeth is only two steps below the throne - and he deeply wants to become a King. Still, he isn’t ready to betray his oaths and murder the King he promised to faithfully serve, he is afraid to make this step. That’s why he asks the stars - that were often considered the eyes of angels in Heaven - to hide, so that his desires would stay hidden.
Another possible explanation of this phrase is the mere wish of the author to keep the intrigue. The audience shouldn’t know that Macbeth is going to murder King Duncan from the very beginning, so the character doesn’t state explicitly what he is going to do.
Also, we can interpret this phrase as the voice of consciousness. Macbeth is ashamed of his desire, that’s why he asks the stars to turn away and not look at him - because Macbeth feels condemned by the stares of the “angels” he feels.