When Macbeth first encounters the witches in Act I, Scene III, he is curious and intrigued by their presence. He asks what they are, for example, and wants to know more about their prophecies. He is also confused as to how these prophecies might come true.

Macbeth meets with the witches again in Act IV, Scene I.  Remember that this time, Macbeth deliberately seeks them out. His attitude is very demanding: he insists that they answer his questions about the future. Moreover, he says he does not care what they have to do to provide these answers; he even tells them to summon their masters.

When he has received the answers he seeks, he thanks the witches for their advice ("good caution") and claims that if he had three ears, he would listen with all three.

It is clear, then, that Macbeth's reaction has changed considerably. He has moved from a position of interest to one of dependence. He believes wholeheartedly in what the witches tell him and needs their guidance to rule. 

In the beginning of the play, Macbeth was in awe of the witches.  There was a sort of respect for them and their visions.  Now in Act IV, scene 1, Macbeth scorns them and insults them when asking for the answers to his questions.  He demands (conjures) them up and then wants answers right then and there.

"How now, you secret, black, and midnight hags!  What is't you do?  I conjure you, by that which you profess, Howe'er you come to know it, answer me"

He is very demanding and expects them to give him what he wants.  Then when the apparitions appear he expects them to speak with him, not to him.  The first witch instructs him to be quiet.  She tells him they read his thoughts.  He still tries to command the apparitions to tell him more.  This is very different from the Macbeth who met the witches in the beginning.