Passage
So they smote him, and his sons and all his people, until there was none left him remaining: and they possessed his land.
So they smote him, and his sons and all his people, until there was none left him remaining: and they possessed his land.
Numbers 21:33 And they turned and went up by the way of Bashan: and Og the king of Bashan went out against them, he and all his people, to battle at Edrei.
Numbers 21:34 And Jehovah said unto Moses, Fear him not: for I have delivered him into thy hand, and all his people, and his land; and thou shalt do to him as thou didst unto Sihon king of the Amorites, who dwelt at Heshbon.
Numbers 21:35 So they smote him, and his sons and all his people, until there was none left him remaining: and they possessed his land.
The verse centers on "smote", "sons", "people", "until", "none", "left", "remaining", and "possessed". It is saying that the verse draws attention to "smote" and "sons", so its meaning should be read from those terms before moving to application.
The prior verse says "And Jehovah said unto Moses Fear him...", giving immediate footing for "smote" and "sons". In Numbers context, the local focus is covenant, worship, and faithfulness.
A plain takeaway is to answer the verse's own emphasis on "smote" and "sons" with trust shaped by these words, not by a vague optimism outside the passage.