Romans 9

16 So it is God who decides to show mercy. We can neither choose it nor work for it.
  17 For the Scriptures say that God told Pharaoh, "I have appointed you for the very purpose of displaying my power in you and to spread my fame throughout the earth."18 So you see, God chooses to show mercy to some, and he chooses to harden the hearts of others so they refuse to listen.
  19 Well then, you might say, "Why does God blame people for not responding? Haven't they simply done what he makes them do?"
  20 No, don't say that. Who are you, a mere human being, to argue with God? Should the thing that was created say to the one who created it, "Why have you made me like this?"21 When a potter makes jars out of clay, doesn't he have a right to use the same lump of clay to make one jar for decoration and another to throw garbage into?22 In the same way, even though God has the right to show his anger and his power, he is very patient with those on whom his anger falls, who are destined for destruction.23 He does this to make the riches of his glory shine even brighter on those to whom he shows mercy, who were prepared in advance for glory