Chapter 4 locates the start of the Kingdom of Heaven in a particular kind of interior integration. The kingdom begins where the heart becomes resolved enough that mind and body stop pulling in different directions.
That makes the kingdom less like a place one waits for and more like a quality of alignment one enters. Outer conditions matter, but they cannot substitute for the inward union that makes heaven livable.
The point is not private self-mastery for its own sake. It is becoming the kind of person who can harmonize with God’s order when it comes.