In Act I of Macbeth, how significant is the change we see in Macbeth?
The change in Macbeth is essential to the remainder of the play. Before he hears the witches' prophecy, Macbeth is a loyal and brave soldier who serves and protects King Duncan. He is known for his strength and courage. As the play opens, Shakespeare establishes this when the Captain describes how fiercely Macbeth fought in the recent battle against the forces of the King of Norway that had attacked Scotland. Duncan even rewards Macbeth for his loyalty.
After the witches tell Macbeth he will be King of Scotland, Macbeth at first refuses to even consider it. It seems so outlandish. Then he assumes the attitude that if he is to be king, then it will happen without any effort on his part.
Finally, by the end of the Act I, Macbeth's ambition is fully aroused, and he is thinking in terms of what he must do to become king very soon. Macbeth has changed from a loyal defender of King Duncan to an ambitious man who secretly wants the throne himself and is prepared to take it. This profound change in Macbeth leads to Duncan's murder and Macbeth's eventual destruction. If Macbeth had remained loyal to his king, the tragedy would not have occurred.