1)
What is the meaning of "His'arev Na"?
1.
Rashi: Wager.
2)
What are "Rochevim"?
1.
Radak: They are soldiers to ride on them.
3)
Why did he mention not having riders for the horses?
1.
Malbim (Yeshayah 36:8): Mitzrayim will not save you. They will only give to you chariots and horses. You need riders for them, [and you do not have]!