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.
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. 1
See Oznayim la'Torah on the current Pasuk.
