How does Macbeth's attitude toward the witches in Act 4 contrast with his first encounter with them? What does this show about his character?

At first, Macbeth was skeptical of what the witches had to say to him.  While it was interesting for him to hear (in the same way a good horoscope or fortune in a fortune cookie would be) he didn't pay it much mind.

Now that he has taken it upon himself to become king and fulfill the other "prophecies" the witches have made, Macbeth is eager to hear more.  It's almost as if the witches' prophecies give him an excuse for commiting horrible deeds.

Macbeth begins the play as a noble and loyal solider. He has now become power hungry and a believer in "black" magic.