Final answer:
Macbeth contemplates murdering King Duncan and becoming king, revealing his deep ambition and moral struggle. Despite his fear and recognition of the deed's evil, his desire for power fuels his consideration of regicide.
Step-by-step explanation:
The suggestion that comes to Macbeth's mind is the idea of murdering King Duncan in order to become king himself. This internal conflict indicates Macbeth's ambition and the beginning of his moral decline, as he wrestles with the notion of committing regicide, which goes against nature and his conscience.
Macbeth's hesitation and fear demonstrate the gravity of the deed he contemplates, revealing the tumultuous emotional state that the witches' prophecy has provoked within him. Despite recognizing the evil of his thoughts, Macbeth's ambition is so strong that it begins to cloud his judgment, as his mind is 'smother'd in surmise' and he is drawn into considering the murder.
The horrid image that scares Macbeth enough to make his hair stand on end and his heart pound represents the terrifying nature of his own thoughts about killing Duncan. The fact that this violent thought comes so readily to Macbeth after the witches' prophecy suggests that deep within, he has a latent capacity for ruthlessness and a strong desire for power.