Charles Ellicott Commentary Numbers 22:3

"And Moab was sore afraid of the people, because they were many: and Moab was distressed because of the children of Israel." — Numbers 22:3 (ASV)

And Moab was sore afraid of the people.— There was no ground for this apprehension, since the Divine command given to Moses was Distress not the Moabites, neither contend with them in battle (Deuteronomy 2:9). It does not appear, however, that Balak was aware of the prohibition; and the recent conquests of the Israelites naturally filled the Moabites with alarm, especially since when the Israelites sent to the King of Moab to ask permission to pass through his land, he did not consent (Judges 11:17).