What does the Bible say about Repentance?

Acts 17:28-31
 28.  For in him we live, and move, and have our being; as 
      certain also of your own poets have said, For we are 
      also his offspring.
 29.  Forasmuch then as we are the offspring of God, we ought 
      not to think that the Godhead is like unto gold, or silver, 
      or stone, graven by art and man's device.
 30.  And the times of this ignorance God winked at; but now 
      commandeth all men every where to repent:
 31.  Because he hath appointed a day, in the which he will 
      judge the world in righteousness by that man whom he hath 
      ordained; whereof he hath given assurance unto all men, 
      in that he hath raised him from the dead.

 Matthew 21:28-29
 28.  But what think ye? A certain man had two sons; and he came 
      to the first, and said, Son, go work to day in my vineyard.
 29.  He answered and said, I will not: but afterward he repented,  
      and went.

Romans 2:4
  4.  Or despisest thou the riches of his goodness and forbearance 
      and longsuffering; not knowing that the goodness of God leadeth 
      thee to repentance?

      That's what the Bible says.