What is the meaning of "v'Yad Hashem"?
Rashi citing Targum Yonasan: A spirit of Gevurah from Hashem. He was able to run on foot in front of the chariot [Radak - even though Achav began traveling first. Eliyahu was in front all the way to Yizre'el.
What is the meaning of "va'Yshanes"?
Rashi: He girded. There is nothing like this [in Tanach]. It just comes to show zealousness, like a Gibor.
Why did Eliyahu run in front of Achav?
Rashi citing Zevachim 102a: This was lest Achav go alone. He honored the king.
Why does it say "Bo'achah"?
Radak: This 'addresses' one who knows the way (until you get there). We find like this - "Bo'acha Minis" (Shoftim 11:33), "Bo'achah Ashurah" (Bereishis 25:18).
QUESTIONS ON RASHI
Rashi writes that Eliyahu honored the king. Why did he do so only now?
Malbim: Now Achav leaned [to serve Hashem] after Eliyahu; he repented. Eliyahu thought to bring him to serve Hashem.