Charles Ellicott Commentary Deuteronomy 2:30

"But Sihon king of Heshbon would not let us pass by him; for Jehovah thy God hardened his spirit, and made his heart obstinate, that he might deliver him into thy hand, as at this day." — Deuteronomy 2:30 (ASV)

The Lord your God hardened his spirit, and made his heart obstinate. —Jehovah gave the strength to Sihon, as He had done to Pharaoh, and as He does to all. Sihon was responsible for using the strength which God gave him in opposition to the Divine purposes. To “harden” a man’s spirit is not necessarily a moral process any more than the hardening of steel. “Made obstinate” is the same verb used in Joshua 1:6, for “Be of a good courage.” An unyielding spirit and a courageous heart are good or bad according to the use made of them. Sihon used them badly, Joshua used them well. God’s gifts were the same to both. (See also Joshua 11:20.)