1)
Why did they say Elokim came to the camp?
1.
Malbim: [They knew that] Hashem dwells on the Aron.
2)
Why were they afraid?
1.
Malbim (7,8): (a) Until now, we fought with people, and now, with Hashem their Savior. (b) Not only do we have no chance to win. Further, we will perish, like Hashem wiped out the Egyptians!