Macbeth is fearing what will happen to him in the life to come, with thoughts of an undetermined destiny which worry him while his evil deeds may come back to him. Dramatic Irony is exemplified when the King thinks he is honouring him with his stay, while Macbeth and his Lady are plotting to murder him, "...as his host, who should against his murder shut the door, not bear the knife myself...".
Mixed emotions run through Macbeth's mind as he is mid-struck between Duncan's fate. His uncertainty pertaining this matter builds upon his guilt of the thought of betraying his friends trust. Towards the end of his soliloquy, he begins to use vocabulary that describe and display the image of heavens in the after-life. "Will plead like angels, trumpet-tongued...". Macbeth's speech appears to be delivered in a steady manner, showing his thoughts are flowing endlessly about the assassination.
Within the limit of Act I, Macbeth has shown the audience his different personalities. Lady Macbeth's power convinces and persuades Macbeth to follow her stubborn ways. She is convinced they can't fail as long as they find the courage to just go ahead with their plan.