What did Og - who preceded the Flood (which took place aalmost eight hundred years earlier) - do to merit to live so long?
Rashi: See 21:34:2:1*.
Targum Yonasan: When Og saw that Avraham and Sarah could not have children, he would mock them, comparing them to trees that are planted beside pools of water but which does not produce fruit. Consequently, Hashem let him live to see how Avraham's descendents had multiplied and then to fall into their hands.
Why did Hashem need to instruct Moshe not to be afraid of Og any more than Sichon?
Rashi (citing a Midrash) and Ramban #1: Because Moshe was initially afraid that Og's merit 1 would stand him in good stead. 2
Ramban #2: Because, since Moshe did not plan to capture the lands of Sichon and Og, 3 he was about to veer away from Og as they had done regarding Edom; so Hashem instructed him not to be afraid but to go ahead and take up the challenge.
Ramban #3 (citing a Midrash): Because Moshe was afraid that Yisrael had somehow sinned during the war with Sichon. 4
Rosh: There was no one as strong as him. 5 Only he "remained from the remaining Refa'im" (Devarim 3:11). 6
Oznayim la'Torah #1: Because he was equal in strength to his entire army. 7
Oznayim la'Torah #2: Because, whereas before he attacked Sichon, Hashem had reassured him not to fear him, here, when Og attacked suddenly, He had not yet done so.
Rashi: In that he informed Avraham that Lot was captured (See Bereishis, 14:13), as a result of which Avraham fought with the four kings and freed him. Ramban - otherwise, it is inconceivable that Moshe - who warned Yisrael not to be afraid of the Cana'anim (Devarim 31:6, 1:29-30), should be afraid of flesh and blood.
See Sifsei Chachamim.
Ramban: As is the way of Tzadikim, like we find by Yehoshua. See Yehoshua, 8:1. Refer also to Bereishis, 32:11:1:1. Moshe was afraid in spite of the fact that the battle with Og took place after Yom Kipur and Sukos. See Oznayim la'Torah:
Oznayim la'Torah (in Devarim): According to the Yalkut Shim'oni he was the strongest man who ever lived.
The Ramban proved that Moshe could not fear human strength (refer to 21:34:2:1*)! Perhaps the Rosh holds that Moshe feared that an overt miracle would be needed, and Yisrael did not have enough merits. Or, he feared lest B'nei Yisrael fear Og, and due to this, they will be punished. Or, he assumed that Og's awesome strength must be due to great merits. (PF)
Why does the Torah write "Nasati oso", in the past tense?
Riva: Hashem had already decided to deliver him into the hands of Moshe from the days of Avraham.
QUESTIONS ON RASHI
Rashi writes that Moshe feared Og's merit, that he informed Avraham that Lot was captured. - But his intentions were bad; he wanted Avraham to be killed, so that he would be able to take Sarah?
Da'as Zekenim, Hadar Zekenim, Moshav Zekenim: Since salvation came from it, he was afraid. We find that Rus came from Balak as reward for the 42 Korbanos he brought, even though he intended for evil, to curse Yisrael (Horiyos 10b).
