There are many theological threads in this introduction to the Sermon on the Mount, here I want to settle on just three points which will resonate through the rest of the Sermon.
The Kingdom of God. There is an eschatological promise in the beatitudes; there is coming a time when the people of God will experience a reward for their oppression and perseverance (Allison, The Sermon on the Mount, 42). These promises are all related to the hope for a restored kingdom for Israel in the future.
Here is but one example of dozens of texts in the prophets with similar expectations. The conclusion to the first half of the book of Isaiah begins with a judgment of the nations using Edom as a model of Israel’s enemy. Isaiah 34:2-4 describes an apocalyptic judgment on the nations. The Lord will utterly destroy them, they will wither like leaves on the vine. But in 34:16-16 the Lord gathers his people back to their allotment and “they will possess it forever.” Feeble hands will be made strong, the eyes of the blind will be opened, the deaf will hear, the lame will leap, and the mute will speak (35:5-6). The way to Zion will be opened and the redeemed will travel this “way of holiness” in gladness and joy (35:9-10). The prophets anticipate Israel’s liberation from her enemies but also a time of Edenic peace and prosperity.
Although the kingdom is in many ways still future (from both the perspective of Jesus and the present church), there are some aspects of that kingdom immediately present in the ministry of Jesus. Immediately following the Sermon, Matthew collects a series of stories which indicate the Kingdom of God is in some ways present in Jesus’ ministry. For example, the first story is the healing of a man with leprosy. Jesus makes him clean, the verb (καθαρίζω) is cognate to the noun used in Matthew 5:8, the “pure (καθαρός) in heart.” Although this man is made clean physically, he has “seen God” in Jesus.
In Matthew 11:1-5 disciples of John the Baptist ask Jesus if he is the messiah, and Jesus responds by pointing to the many miracles and healings which bear witness to a messianic outpouring of the Spirit of God. In 11:6 he concludes by pronouncing a blessing on those who do not stumble on account of him.
The kingdom is therefore present in the ministry of Jesus in a very real way. People are experiencing the presence of the king. These are a foretaste of the kingdom expected in by prophets in the Hebrew Bible.
Reversal of Expectation. “The beatitudes “present true human flourishing as entailing suffering as Jesus’s disciples await God’s coming kingdom that Jesus is inaugurating” (Pennington, Sermon on the Mount, 153). In each of the beatitudes there is a reversal of what the outside might think is the way to receive blessing from God. The obvious example is the blessing pronounced on those who suffer for the sake of Jesus.
Suffering is not usually something people rejoice in, so to say, “the way to flourish as a human is to suffer for the sake of Jesus” would have surprised, even shocked the Jewish listener who would see suffering as a sign of judgment for sin. A later Greco-Roman reader would also consider this a strange saying since the pursuit of honor in the Roman world left little room for suffering on account of a crucified criminal!
Redefining Happiness. The form of a beatitude implies the one who does part one of the saying will be happy because part two of the saying will make them happy. But as Scot McKnight observes, these sayings are not descriptions of happiness in the modern sense of the word. Just google “how to be happy” as see all the pages listing “fifteen ways” to be happy: smile, meditate, spend time outside (on the warm day) or with friends, practice gratitude, etc. Although these are all very good things to consider, they are not at all what these eight beatitudes describe as happiness. Modern happiness tends to be focused on my personal happiness, feeling good about myself.
These eight beatitudes are all other focused, being a peacemaker is not about your personal happiness but rather reconciling others; one cannot “show mercy” without acting on behalf of others.
In addition, these beatitudes redefine happiness as future oriented. Even if this exact moment seems oppressive and difficult, the person truly seeking the will of God always has confidence the struggle is worth it because God is working in history to re-establish his order on the chaos of creation. If we focus our happiness on ourselves and this particular moment, then we will probably not be total happy.