He said therefore to the crowds that came out to be baptized by him, "You brood of vipers! Who warned you to flee from the wrath to come?
Bear fruits in keeping with repentance. And do not begin to say to yourselves, 'We have Abraham as our father.' For I tell you, God is able from these stones to raise up children for Abraham.
Even now the axe is laid to the root of the trees. Every tree therefore that does not bear good fruit is cut down and thrown into the fire." (ESV)
The above passages record a time in the ministry of John the Baptist. Part of John's ministry was a baptism unto repentance.
The Gospel of Matthew (c.f. Matthew 3:7-10) records that some of those who were coming out to see the ministry John were members of the religious leaders of Israel, the Pharisees and the Sadducees. John knew that these men did not come out because they knew that they were in need of repentance in their lives. These leaders believed that they had a privileged relationship with God because of their biological ties to the patriarch Abraham. They also thought that they were right with God because of their own keeping of the Law of God. Telling them that they were in need of repentance, and that they were alienated from God, and were actually children of His wrath, was an insult to them.
Most of those around us, who do not know Christ as Savior, see themselves as "good" people. Telling a lost person that they are sinners with wicked hearts, and are in need of repentance, and a turning to the finished work of Jesus Christ for their salvation, is a great insult to them. But, they need to be told this.
Again, as I pointed out in Monday's post http://michael-hotard.blogspot.com/2011/01/journey-through-gospel-of-luke-prepare.html , a person needs to be confronted by the Law before they can ever see their need for a savior. They must hear the bad news before they hear the Good News.