Why should the entire land fear Hashem?
Radak: He prepared the land to be settled - "Kones ka'Ned Mei ha'Yam" (verse 7).
Malbim: Via the fixed natural conduct, they fear Hashem, for He created everything.
Is the second half of the verse a repetition of the first?
Radak implies that it is. (He often says that matters are repeated in different words, to strengthen them. - PF)
Malbim: No. The first half teaches that the fixed natural conduct mandates fear of Hashem, for He created everything. The second half teaches that conduct via Hashgachah, which conducts the settled part of the land, imposes Magur, which is greater than Yir'ah. It is fear of reward and punishment. All should fear lest He make the sea water flood the land, or withhold rain!