Why were the unspecified men who left over Manna until the morning?
Rashi and Targum Yonasan: They were Dasan and Aviram. 1
Sifsei Chachamim: Because wherever the Torah uses the word "Anashim" or "Nitzim" it refers to them.
Why does the Torah first record the Manna turning wormy, and then going bad?
Rashi: The Torah inverts the order, as if to say that the Manna turned wormy after having gone bad.
Ramban #1: Because, bearing in mind that the Manna going bad and wormy was in itself a miracle, it is not surprising that it turned wormy first before going bad. 1
Ramban #2 (citing the Midrash): Hashem delayed it from going bad, to avoid the people from having to bear the bad smell of rotting food.
Gur Aryeh: We can explain slightly differently than Rashi. Usually, a decaying item starts to smell a little bad, and worms grow, and only afterwards does it go completely rancid. Our Pasuk is telling us that the Manna that was left over had already reached that final rancid stage. 2 Later, Pasuk 16:24 tells us that the Manna that they left over for Shabbos did not even begin to smell bad. 3
Ramban: Proof of this lies in Pasuk 16:24 below, where the Torah writes that on Shabbos, the Manna did not go bad, nor did it [even] become wormy - a proof that when it did go bad - refer to 16:24:1:1 - it became wormy first (see Ramban).
Gur Aryeh: Had our Pasuk written only "va'Yiv'ash," I may have thought it only reached the initial stage of smelling a little bad. It therefore first states "va'Yarum Tola'im," telling us that it reached the final rancid stage.
Gur Aryeh: Similarly, had Pasuk 16:24 written only "v'Lo Hiv'ish," I might have thought that on Shabbos, the Manna did not go completely rancid, but did smell a bit. Therefore it continues "v'Rimah Lo Hayesa Bo" - and if there were no worms, it goes without saying that it did not go rancid! It must be saying that there wasn't even a little bad smell.
The Gemara (Arachin 15a) counts leaving over the Manna as one of the ten Nisyonos in which our forefathers tested Hashem in the wilderness (see Avos 5:4). What is their sequence; and why are they called "tests," rather than "sins"?
Refer to 16:3:2:1.
QUESTIONS ON RASHI
Rashi writes: "Anashim - [this refers to] Dasan and Aviram." But Rashi writes elsewhere that the word "Anashim" implies important people (see Rashi to Bamidbar 13:3). Clearly, Dasan and Aviram were not upstanding individuals, or worthy of any honor!
Gur Aryeh 1 (to Shemos 2:13): "Anashim" (or the singular 'Ish') means a master of some thing or some trait. While the term is usually used in praise of an upstanding person, it can also be used to denigrate a villain, as a "master of evil deeds" -- depending on context. 2
Also see Mizrachi (loc. cit.) - Refer to Shemos 2:13:1.01:1 .
Also see Gur Aryeh (to Devarim 1:13) - The term "Anashim" (as opposed to "Nashim") implies someone who takes action, as opposed to frailty or inaction. Thus "Anashim" means people who have distinguished themselves (for good or for evil). Furthermore, "Anashim" conveys the trait of Gevurah. In a good sense, this means people who fear Hashem and overcome their Yetzer ha'Ra; yet it could also mean people who are quarrelsome and try to overpower others (as it does in this case; also see the following question).
Rashi writes: "Anashim - [This refers to] Dasan and Aviram." How do we know it was they?
Gur Aryeh (to Shemos 2:13): The Pasuk refers to the men as "Anashim," which in this context implies "masters of evil deeds" (see the preceding question, 16:20:1.1:1 ). This act of leaving over the Manna was not their only crime; it must have been people who were generally evil - such as Dasan and Aviram, whose streak of rebellion ultimately culminated in their showdown against Moshe during Korach's rebellion. 1
Fur further insights from Maharal, refer to Shemos 2:13:1.02:2 and 2:13:1.03:2 .
Rashi writes: "Anashim - [this refers to] Dasan and Aviram." What was with Dasan and Aviram; why were they constantly antagonizing Moshe?
See Shemos 2:13:1.03 , where we cite several works of the Maharal that address this question.