1)
Why did Melech Yisrael go out only now?
1.
Radak: He waited until Na'arei Sarei ha'Medinos and some of the [7,000] soldiers started striking Aram, and he saw that the salvation began. Until now he was in doubt, until he saw Aram flee. Now he and the rest of the [7,000] went out and chased Aram.
2.
Malbim: Until he saw them flee, he was afraid to leave the city.
2)
How did they strike the horses and chariots?
1.
Radak: They struck the horses and toppled the chariots; the riders fell, and [Yisrael] struck them. They struck the horses and chariots only due to the riders fleeing on them; had they caught them, they would not have struck the horses and chariots.
