After Nadav and Avihu died it says, “V’Chol Bais Yisroel Yivku Es Hasreifa Asher Saraf Hashem; the entire nation will cry and extinguish the raging fire that hashem burned.” (Shemini 10:6) What are these fires and what does it have to do with the death of a Tzaddik?
The Pninim MiShulchan Gavoa brings that at the Levaya of the Vilna Gaon, the Chayei Adam, Rav Avhrohon Danzig, said that the Midas HaDin, which is like a raging fire, constantly prosecutes Bnei Yisrael. The way to extinguish this fire is with water, the water of Torah.
While the tzadikim are alive, their Torah keeps the fire at bay and prevents it from devouring Klal Yisrael. Upon their death, the water stops to flow, and the fire can grow out of control, causing great damage to Klal Yisrael. The only thing that extinguishes this fire are the tears that run from our eyes upon the news of their passing. Hashem tells Klal Yisrael to cry rivers of tears for the Tzaddikim as a way of saving ourselves, despite the loss of our water filled protector.
taken from revach.net