Why the Giant King Sihon Fell Before Israel by Torah's Merit

"And the LORD said (unto Moses) [unto me]: See, I have begun to give Sihon and his land before you" (Deuteronomy 2:31). [And it is written:] "And I destroyed the Amorite [from before them, whose height was like the height of the cedars]" (Amos 2:9). By virtue of what? By virtue of the Torah, which the sages teach. Our Rabbis said: Sihon was strong; his height was like a wall-tower, and he was stronger than all creatures, and taller than every tower in the world, yet his feet reached the ground. And no creature was able to stand before him, as it says: "And I destroyed his fruit from above [and his roots from beneath]" (ibid.). What did the Holy One, blessed be He, do? He bound the prince that belonged to him and to his land, and cast him down (in his place) [from his place], and handed him over before Israel. Our Rabbis said: Sihon, and even more so, was harder than Pharaoh and his armies. And just as they uttered a song over the downfall of Pharaoh, so were they fit to utter a song over their downfall. But David came and uttered a song over them, as it is said: "To Him who smote Egypt through their firstborn" (Psalms 136:10); "To Him who smote great kings... Sihon king of the Amorites..." (ibid. 136:17, 19).