"The crowd listening to the Sermon on the Mount did not expect what they got. While we may know the common phrases from Jesus's discourse, the audience came away surprised, and the reason for that surprise involved battered expectations.
Old Testament prophecies pointed to the coming of a Messiah: the descendent of David, the Child of a virgin, the suffering Servant. However, as often can happen with God's Word, the teachers in ancient Israel twisted the prophecies to meet their own preconceived notions. Many did not recognize the Messiah (the promised one) when He arrived. Instead, they misunderstood His mission and willfully distorted the promises of God (cf. John 11:49-50).
When Jesus taught the crowds, He had to deal with the flawed concept of the people. They expected a political leader to lead them out of Roman occupation and not necessarily the bondage of sin; they wanted someone who had compassion for the Jews and Gentile converts alone; and they thought that being a descendent of Abraham was reason enough for the Messiah to accept them." Read more about the Sermon on the Mount from Doug Bookman