But Sihon king of Heshbon would not let us pass by him: for the Lord thy God hardened his spirit, and made his heart obstinate, that he might deliver him into thy hand, as appeareth this day. (Deuteronomy 2:30)
He was suspicious of their sincerity and questioned the reasonableness of their request (see Num. 21:23).
Hardened his spirit.
That is, allowed Sihon’s obstinacy to run its course.
Made his heart obstinate.
The Hebrew verb thus translated means “to be strong,”“to be stout,”“to be firm.” It is elsewhere translated “strengthen” (Deut. 3:28; Ps. 27:14), “confirm” (Isa. 35:3), “fortify” (Nahum 2:1), “was stedfastly minded” (Ruth 1:18). The Lord would not interfere with the natural operation of Sihon’s heart and intents, but would confirm him in it (see on Ex. 4:21). One may use the God-given strength of mind and heart to continue in the wrong or to turn to the right. The Lord does not force a man to the one or to the other, but ever stands ready to cooperate by His Spirit with the man who chooses the good. The same word is translated in Joshua 1:6 as “be ... of a good courage.”