Esau hated Jacob because of the blessing with which his father blessed him. Esau said in his heart, “The days of mourning for my father are at hand. Then I will kill my brother Jacob.”
The LORD says: “For three transgressions of Edom, yes, for four, I will not turn away its punishment, because he pursued his brother with the sword and cast off all pity, and his anger raged continually, and he kept his wrath forever;
then Israel sent messengers to the king of Edom, saying, ‘Please let me pass through your land;’ but the king of Edom didn’t listen. In the same way, he sent to the king of Moab, but he refused; so Israel stayed in Kadesh.
But Sihon didn’t trust Israel to pass through his border; but Sihon gathered all his people together, and encamped in Jahaz, and fought against Israel.