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.
But Jesus struck through each of these concepts. Instead of rallying an earthly overthrow of Rome, He called those who suffered oppression blessed. Worse still, He called on them to love those who oppressed them, who ruled them, who cursed them—not just compassion for other Jews and converts, but to everyone. On top of all that, Jesus told them that not just anyone could enter the Kingdom of Heaven—no matter how many miracles they perform in His name—but only those who do the will of the Father.
By the end of the Sermon, the listeners came away amazed and likely stunned. All they'd been told, all they expected about the Messiah, had been poignantly corrected.
Adapted from the lecture notes of Dr. Doug Bookman, professor of New Testament Exposition at Shepherds Theological Seminary (used by permission).