What makes it fun are the strange, contradictory, and confusing statement Jesus makes. Christians spend a lot of time and energy analyzing the Sermon on the Mount, but a lot of it doesn't make sense. A believer might pray for understanding, or believe whatever their denomination says.
Verses 3 through 12 are called the Beatitudes, or blessings. Basically, the beatitudes say, hey, don't worry, if you don't have it now, you'll get it later. If you're poor in spirit, you get the kingdom of heaven; if you're in mourning, you'll be comforted; if you're meek, you'll get the earth; if you aren't getting righteousness, you'll get it later.
Those verses--3 through 6--cover people who are lacking something. In verses 7 through 11, Jesus addresses people who have good qualities and says they'll be rewarded. So if you're merciful, you'll be shown mercy; if you're pure in heart, you'll see God; if you're a peacemaker, you'll be called children of God; if you're persecuted because you do the right thing, you'll get the kingdom of heaven.
In verses 11 and 12, he expands on the idea of people who are mistreated. "Blessed are you when people insult you, persecute you and falsely say all kinds of evil against you because of me. Rejoice and be glad, because great is your reward in heaven, for in the same way they persecuted the prophets who were before you." I'm sure this verse brought solace to centuries of Christian martyrs, but I've also had it quoted at me by Christians who felt I wasn't getting their message. Encouraging martyrdom in this life because things will be better in the next (imaginary) life after death was one of Jesus's worst ideas.