What is the meaning of "Vayaronu"?
Rashi and Targum Onkelos: It means 'and they praised (Hashem)'.
Targum Yonasan: It means 'and they thanked (Hashem)'. 1
For responding to their request or for pardoning their sin (of the Golden Calf) and resting his Shechinah among them (Rashi in Shir ha'Shirim - though he translates "Vayaronu" as 'and they praised', as he does here.
What is the sequence of this Pasuk and the following two Pesukim?
Rashbam: After Moshe and Aharon entered the Ohel Mo'ed to pray, the fire descended and proceeded to burn the Ketores on the Mizbe'ach ha'Zahav. There it struck Nadav and Avihu, who had come to ignite the Ketores with their fire before burning the Ketores, following which it moved to the Mizbe'ach ha'Olah to burn the Olah and the Shelamim.
Why did they fall, and what [praise] did they say?
Moshav Zekenim: We learn what is not explicit from what is explicit. 1 It says [when] Eliyahu [defeated Nevi'ei ha'Ba'al] "va'Yiplu
Moshav Zekenim asked why they fell, and did not answer. Perhaps he means, for the same reason they fell there. Metzudas David says there, they fell to bow to Hashem. (PF)