The promise is stunning and, at first, confusing. God has committed to dispossess the Canaanite nations before Israel. Why not do it all at once?
Targum Pseudo-Jonathan on Exodus (Exodus 23:29) answers the question Israel was afraid to ask: I will not expel them before thee in one year, lest the land become a wilderness, and the beasts of the field multiply upon thee, when they come to eat their carcasses, and injure thee.
The Ecological Logic of Slow Conquest
A sudden emptying of the Land would create a vacuum. Fields would lie fallow. Villages would stand unoccupied. The wild would reclaim what human hands used to tend. Lions, bears, boars — the predators that always lurk at the edges of civilization — would multiply in the empty spaces.
And more darkly: they would feast on the unburied dead. When they come to eat their carcasses. A battlefield full of corpses draws scavengers. Scavengers that learn human flesh then learn to hunt the humans who come after. The Torah is describing a very specific ancient fear — a land too quickly depopulated becomes dangerous in ways the conquerors did not anticipate.
The Pace of Redemption
There is a deeper lesson here. God does not always deliver in one stroke. Gradual redemption is also divine wisdom. Israel must grow into the Land — must increase in population, in competence, in readiness — before receiving the full inheritance.
The Takeaway
Sometimes what looks like delayed blessing is actually protective blessing. The Torah trusts God's timing — and teaches that the slow fulfillment of a promise is often wiser than the fast one.