From: Matthew 21:28-32
The Parable of the Two Sons
(Jesus told the chief priests and the elders,)  "What do you think? A man had two sons; and he went to the first and said, 'Son, go and work in the vineyard today.'  And he answered, 'I will not'; but afterwards he repented and went.  And he went to the second and said the same; and he answered, 'I go, sir,' but did not go.  Which of the two did the will of his father?" They said, "The first." Jesus said to them, "Truly, I say to you, the tax collectors and the harlots go into the kingdom of God before you.  For John came to you in the way of righteousness, and you did not believe him, but the tax collectors and the harlots believed him; and even when you saw it, you did not afterward repent and believe him.
32. St. John the Baptist had shown the way to sanctification by proclaiming the imminence of the Kingdom of God and by preaching conversion. The scribes and Pharisees would not believe him, yet they boasted of their faithfulness to God's teaching. They were like the son who says "I will go" and then does not go; the tax collectors and prostitutes who repented and corrected the course of their lives will enter the Kingdom before them: they are like the other son who says "I will not", but then does go. Our Lord stresses that penance and conversion can set people on the road to holiness even if they have been living apart from God for a long time.
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland.
Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.