Numbers 21:34
And the LORD 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, which dwelt at Heshbon. And the LORD 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, which dwelt at Heshbon.
The Lord spoke to Moses not to be afraid of Og, king of Bashan, for He had delivered Og together with all his people and his land into Israel's hand, and Israel was to do to him just as had been done to Sihon king of the Amorites who dwelt at Heshbon. That divine assurance gave Moses confidence to lead Israel forward against the giant king and his powerful army. It emboldened him to face even a seemingly secure fortress, trusting that what God had promised would be accomplished.
In contrast to the earlier defeat when the people had acted against God's command without their appointed leader and without the signs of God's presence, Israel now advanced in obedience with Moses, the cloudy pillar, and the ark. Trusting God for deliverance, they moved forward under His leading. Because the Lord led them and fought for them, they conquered Og's forces and his land in a complete victory.
That victory over Bashan confirmed that God was with Israel and gave the people assurance for the future. Thus Israel slew two kings before reaching the Jordan, and that slaughter, together with the miraculous staying of the swollen and impetuous Jordan before Israel, filled the kings of the Amorites and the kings of the Canaanites with great terror and melted their hearts with fear. By destroying the Amorites and taking possession of their land Israel proved itself a powerful people, and when Balak and Moab learned of that victory as Israel pitched in the plains of Moab by Jordan near Jericho, they were exceedingly terrified.