What is the meaning of "Red Oso"?
Radak: This is like Imo (with him). Also "va'Yered Oso El ha'Melech" means that he descended Imo and went to the king. The Sar was at the end of the mountain 1 , and Eliyahu was at the top.
It says that the Sar ascended, and Radak explained that Eliyahu descended with him! Perhaps the Sar was at the end of the plateau on top of mountain, and Eliyahu was at the peak. (PF)
Why did Hashem tell him not to fear him?
Radak #1: He feared lest they bring him to the king, for he prophesized that the king will die. Malbim - after Hashem commanded him to go, he was a Shali'ach Mitzvah, and he was not afraid.
Radak #2: He was afraid of Izevel, the king's mother.
