What did Moshe mean when he said "Alei Reish"?
Rashi (in ve'Zos ha'Berachah, 33:23): He meant that it is a Mitzvah to take possession of Eretz Yisrael.
Seforno: He meant that Yisrael had merely to ascend and posess the land since nobody would raise a sword to fight them.
How could they see that Hashem gave the land to them?
Rosh and Hadar Zekenim: Since Hashem brought them to a place of snakes and scorpions, which did not harm them, they could see that He wanted to give them the land.
R. Bachye (citing the Tanchuma): ?Re?ei means understand - and the Pasuk hints at the guardian-angel of the Cana?anim, whom Hashem overpowered in Heaven - a clear sign that the defeat of the Cana?anim on earth was assured. 1 2
Oznayim la'Torah (in Pasuk 19): When they saw the snakes and scorpions that the Pillar of Fire had killed, they knew that Hashem wanted to give them the land and was taking them by the shortest - and most dangerous - route. 3
R. Bachye (citing Devarim Rabah): Because when Hashem punishes a nation, He also punishes its guardian angel. Refer also to 2:31:1:1.
And that is also what the Torah means when it writes - in 2:31 - ?Re?ei Hachilosi Teis Lefanecha es Sichon - Hachel Rash?. See R. Bachye who elaborates.
See Oznayim la'Torah on the current Pasuk.
