What is "Nehar Di Nur"?
Rashi: A river of fire. Malbim ? the river takes fire from Olam ha'Kisei to Olam ha'Galgalim. Chazal said that the river comes from sweat of the Chayos.
What is the meaning of "Naged v'Nafak"?
Rashi: It flows and goes out.
What is the difference between His servants and those who stand in front of Him?
Malbim: The former are Chayos and Sarfei Kodesh prepared to serve the Kisei and bring down influence to the world of the Galgalim. The latter are Serafim that stand in front of the Kisei. They are the supreme Sarim who bring influence below; they are greater than the former.
Which Seforim are open?
Rashi: Seforim of the sins and evil that they did. Malbim ? it is to investigate their deeds and verdict ? "v'Horadti Osam El Emek Yehoshafat."
Ibn Ezra (14): This is like "mi'Sifrecha Asher Kasavta", "va'Yikasev Sefer Zikaron Lefanav."
