1)
Who are "ha'Esanim"?
1.
Radak: They are the strong mountains or hills in Yesod he'Afar.
2.
Radak citing Targum Yonasan: Ikaraya (the primary or initial) [foundations of the land].
3.
Malbim: They are the strong mountains from the days of creation.
2)
What do we learn from "Mosedei Aretz"?
1.
Malbim: They were the foundations of the land when it was 'born' from the Tehom.
3)
What do we learn from "Ki Riv Hashem Im Amo"?
1.
Malbim: Hashem has a quarrel against His nation for sinning against Him. "V'Im Yisrael Yisvakach" to prove that He is vindicated in His quarrel.
