Powtórzonego Prawa 3:2 Komentarz: Rashi & Tze'enah Ure'enah

אל תירא אתו DO NOT FEAR HIM — In the case of Sihon, however, it did not feel it necessary to state, “Do not fear him״!? But in the case of Og Moses feared lest the merit that he (Og) had been of service to Abraham might avail him, as it is said, (Genesis 14:13: see Rashi thereon), "And the fugitive came", and that was Og (Genesis Rabbah 42:8; see Rashi on Numbers 21:34).

“The Lord said to me: do not fear” [3:2]. The Holy One said to Moses: do not be afraid of Og. I gave him into the hands of Israel long ago, in the days of Abraham. Abraham made a banquet for his son, Isaac, when he was circumcised on the eighth day. Og attended that banquet and other nobles were there with him. They said to Og: you said that Abraham would have no children. See how the Holy One has given him a son. Og responded: if I would lay my small finger on him, he would die. The Holy One said: this time you belittle him, you evildoer. You will see so many of his descendants, like the sand in the sea. You will fall into the hands of his descendants. When Israel came to the border of their land, Moses and the Israelites came early before the city of Edrei. They saw Og sitting on top of the wall and Og’s feet reached the ground. The Holy One said to Moses: This is Og, and his feet were thirty-eight ells long. Moses was frightened of him. The Holy One said: do not be afraid. Og took a large mountain and threw it on Israel. Moses took a little earth and recited the Ineffable Name, and the mountain stopped.²⁹Deuteronomy Rabbah, 1.24.

Therefore, our sages also said that it would have been just to recite songs of praise about Sihon and Og, as they did at the Exodus from Egypt regarding Pharaoh. However, King David came and recited songs of praise about them, as the verse says, “Sihon, king of the Amorites, His steadfast love is eternal; Og, king of Bashan, His steadfast love is eternal” [Psalms, 136:19–20].³⁰Yalkut Shimoni, Hukat, Remez, 765 (at the end).