Chapter 4 begins the Kingdom of Heaven inside the person rather than outside them. It says the kingdom starts where the heart becomes resolved enough to unite mind and body and overcome the inner elements of death.
It then rejects the idea that outward religion, martyrdom, or belief are sufficient when they remain self-referential. The kingdom belongs to those who love beyond the self rather than merely seeking a safe private destination.
Finally, the chapter expands heaven from inward reality to familial order. Full heaven is not portrayed as solitary arrival but as restored relational life.