The Sermon on the Mount, like the rest of the New Testament, speaks of the kingdom with a present and a future sense. The Beatitudes refer to the kingdom primarily in its present aspect (5:3, 10) Jesus is saying, this is what kingdom people are like now. In 7:21, however, Jesus is speaking of the Day of Judgment, and the kingdom referred to is the completed, perfected eternal kingdom.
In theological language, the kingdom of heaven is therefore eschatological it relates to the new age, the eternal age, but it is already present in some measure now. At the outset of his ministry Jesus proclaims that the kingdom of heaven is near (4:17, echoing John the Baptiser in 3:2). The sense of the Greek is that the kingdom has come near and is now present in the vicinity, waiting to be populated by the members Jesus will call into it. In that context, 11:12 (the kingdom of heaven has been forcefully advancing) is like a progress report. The kingdom is here and now, and the Sermon on the Mount calls us to make it visible, both individually and corporately.
