Numbers 21:27

Wherefore they that speak in proverbs say, Come into Heshbon, let the city of Sihon be built and prepared:

The verse belongs to the account of Israel's victories over Sihon and Og, in which Israel destroyed the Amorites and took possession of their land. In another description it belongs to the time shortly before Israel entered Canaan when Israel had slain two of the kings of Moab east of the Jordan. The contests with Sihon and Og brought Israel to the same test of faith in which they had failed nearly forty years before, now far more severe because they had to go forward against violent, skillful, and well-equipped armies to possess Canaan. Complete and glorious victory came because they obeyed the command of Heaven to go forward, with Moses with them strengthening their hearts with hope and faith, the Son of God leading the way enshrined in the cloudy pillar, and the sacred ark borne in their midst by priests and Levites.

These recent victories had become widely known and showed that God was fighting for Israel, proving to Balak and Moab that Israel was a powerful people. As Israel moved forward and pitched in the plains of Moab by Jericho, all Moab was in trouble and exceedingly terrified because of what Israel had done to the Amorites. That slaughter, together with the Lord stopping the swollen Jordan before Israel, filled the kings of the Amorites and the kings of the Canaanites with melting fear.