But Sihon king of Heshbon would not let us pass by him: for the LORD your God hardened his spirit, and made his heart obstinate, that he might deliver him into your hand, as it is this day.
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George Leo Haydock
Hardened That is, in punishment of his past sins, he left him to his own stubborn and perverse disposition, which drew him to his ruin. See the note on Exodus vii. 3. (Challoner)
God did not soften his heart, (Menochius) nor make him see the danger to which he was exposing his dominions, by provoking such an army. (Haydock) ...