The dormant merit[1]
ויאמר יקוק אל-משה אל-תירא אתו כי בידך נתתי אתו ואת-כל-עמו ואת-ארצו ועשית לו כאשר עשית לסיחן מלך האמרי אשר יושב בחשבון
Hashem said to Moshe: “Do not fear [Og], as I have given him, his entire nation, and his land into your hand. You shall [be able to] do to him as you did to Sichon, the Aramean King, who dwelled[2] in Cheshbon[3]
After forty years in the wilderness[4], the Jews had begun their final journey towards the land of Israel. They entered the land of Sichon, the King of the Amorites. They successfully conquered his land, and further journeyed towards the land of the Giant Og, King of Bashan. Hashem told Moshe not to fear Og, as their victory was guaranteed. Why was Moshe afraid of Og? There was no reassurance from Hashem before they battled Sichon. It must be that Moshe wasn’t afraid of him, only Og. Rashi brings[5] an explanation from Chazal[6] that Og had actually been alive since the times of Avraham[7]. He informed Avraham that the latter’s nephew Lot had been taken captive during an intense civil war[8]. This knowledge gave Avraham the chance to rescue his nephew, which he successfully accomplished. Moshe was worried that this merit from hundreds of years earlier would grant Og victory over the Jews. Hashem comforted him and told him not to worry, as the Jews would emerge victorious.