The passuk states that Moshe took out all the staffs from before Hashem, “ויראו ויקחו איש מטהו and they saw and a man took his staff.” Onkelos translates the word ויראו “and they recognized,” each man recognized his own staff. The Nefesh HaGer explains b’shem the P’sikta Zutrisi: Moshe brought one board and cut it into twelve pieces, and gave one piece to each Nasi. Each Nasi wrote his name in his own handwriting on his staff and then gave it to Moshe. Moshe put all the staffs together in one group and placed them inside the Mishkan before Hashem. The next day Moshe took out all of the staffs and placed them before the Nesi’im so that they could check and recognize their own handwriting. No one could claim that Moshe erased the Nasi’s name on the staff which flowered and forged Aharon’s name in place. This was done to prove without a doubt that Aharon was indeed chosen, eliminating any possible suspicions.
Earlier in the parsha the pessukim state that Moshe told the 250 followers of Korach to offer ketores together with Aharon in order to prove who the chosen one was. Hashem sent a fire which consumed the 250 men, and Aharon was not touched. What was the need for a second proof after this with the flowering of the stick?
The passuk states after the 250 men were burnt that Bnei Yisrael complained and said, “אתם המתם את עם ה’” which Onkelos translates as “you caused the nation of Hashem to die.” The Ibn Ezra explains that the nation did not accept the proof of the ketores at all. They said to Moshe and Aharon that it was done through their davening or with their wisdom and did not show that Aharon was chosen. The Ramban adds to this p’shat that they said Hashem never commanded Moshe to tell them to offer the ketores, rather he decided this on his own causing them to be burnt. Or the ketores was not a proof since they were punished for offering ketores which Hashem did not command. Bnei Yisrael claimed that Aharon should not be the Kohen Gadol, nor should the Levi’im be the chosen ones. They did not object to the miracle of the ground swallowing up, since Hashem commanded Moshe to tell the gathering, “Move away from being around the tent of Korach and his gathering.” Dasan and Avirom were clearly liable for punishment as Rashi explains, they went out standing tall to curse and blaspheme. Also the passuk states ויקמו לפני משה and they stood in front of Moshe. Onkelos generally translates the word לפני as “before” (קדם); here Onkelos translates לפני as “in the face of,” (לאפי). The Nefesh HaGer explains this reflects the terrible audacity that Korach, Dasan and Aviram had by going out to openly oppose Moshe.
The Ramban explains אתם המתם את עם ה’ differently. Bnei Yisrael said that the 250 men were fitting to serve as Levi’im, not as Kohanim. By having them bring ketores Moshe caused them to die as that is not the avodah of Levi’im. The ketores did prove that Aharon was chosen to be Kohen Gadol, as the ketores was an avodah of the Kohen. However, Bnei Yisrael complained because they were unhappy with the Levi’im being placed instead of the first-borns. They wanted the first-borns from all of the tribes to be able assist the Kohanim with their avodah in the Mishkan, not just the Levi’im. Therefore Hashem told Moshe to speak to Bnei Yisrael to tell them the second proof with the sticks in order to prove that the tribe of Levi was chosen.
Let us remember the miracle of the staff, to constantly have emunas Chachamim!