Why does the Torah insert "Harim"? What is the advantage of mountains over flat terrain?
Rashi: In one Beis-Kur of flat terrain one can plant one Kur, whereas on a mountain one can plant five - four on the slopes and one on top.
What is the significance of the fact that Eretz Yisrael's water supply comes from the rain of the heaven?
Rashi: Refer to 11:10:5:1.
Rashi (in the commentary on the prayer for rain of R. Elazar ha'Kalir that is attributed to Rashi, citing the Sifri): It can be compared to king who drove past a poor man (with reference to other countries) lying on the street, who ordered his servant to sustain him; but when he subsequently drove past a poor man from a respectable family (with reference to Eretz Yisrael) lying in the street, he sustained him personally from his own treasury.
This is also the opinion of the Seforno, who comments on the current Pesukim that Eretz Mitzrayim does not need rain, whereas Eretz Yisrael does - since there are insufficient rivers to provide all its needs - and continues - with a comment on the following paragraph - that the supply of rain depends on whether we keep the Mitzvos or not.