What is the meaning of "va'Lo"?
Rashi: It is a request, like Halevai. Radak - this is like "va'Lo Yelech Na 1 Itanu Amnon Achi" (Shmuel II, 13:26).
How can we learn from that verse? Perhaps there, Na is the request, and va'Lo is said in astonishment! (PF)
Why did Na'aman want earth?
Rashi: He wanted earth of Eretz Yisrael, which is Kadosh, to take to his city to make a Mizbe'ach.
Malbim: He wanted earth from where the Navi stood. He accepted to serve Hashem through [offering] Olah and Zevachim 1 , and not to serve idolatry.
Malbim does not say that he accepted to convert. If so, what are Zevachim? Nochrim may offer only Olos (Menachos 73b)! (PF)
QUESTIONS ON RASHI
Rashi writes that he wanted earth of Eretz Yisrael to make a Mizbe'ach. Could he not take without asking?
Radak: He did not want to make a Mizbe'ach from theft, if not with permission from the Navi and king.