The Sermon on the Mount is filled great controversy. Historically, dispensationalists have seen these teachings/exhortations as futuristic. In other words, they do not apply to a present people, but they are models for the kingdom, which is to come after the seven year tribulation.
Covenant theologians have also been cautious in treating these beatitudes as ethical guidelines for the Christian life. Some fear that taking these assertions too literally may lead to legalism or moralism. After all, biblical laws can only be seen as hypothetical, but never achievable.
The center of this Matthean narrative is necessarily contrary to the previous two assertions. The Sermon on the Mount is an expansion (not an abrogation) of the Mosaic proclamation in the Old Covenant. In fact, one central reason Matthew contains so many mountain allusions is precisely because he is portraying Jesus as the New/Better Moses; the One who brings a message not limited to theocratic Israel, but the theocratic cosmos.
The Beatitudes are not so much about a blessing/cursing motif, but about a shame/honor motif as K.C. Hanson observes. The Sermon was given to bring the new sons of the New Creation into glory and exaltation. They are being honored in this newly created kingdom, where the religious leaders of the day are being portrayed as shameful.
These are not legalistic rules for a future society nor are they the hypothetical ideals of a present society; rather, they are the honorable characteristics of a present society to be lived out in the heavenly kingdom that has come to earth.
 K.C. Hanson How Honorable! How Shameful! A cultural Analysis of Matthew’s Markarisms and Reproaches.