The Gemara in Shabbos (116b) explains how the famous “Nuns” in the parsha (10:35-36) bracket what is termed the two “puraniyos”/punishment: the post-Nuns, obviously, is the Divine fire that arose in response to the national “complaints”. What was the pre-Nuns “puraniyos”? Ramban, quoting this Gemara and several other midrashim, explains the that the “Vayisu MeHar Hashem” in 10:33 was in and of itself a “puraniyos”, as it was that Bnei Yisrael were acting as if they were “tinok boreach mibeis hasefer”: “Lets get away from Har Sinai before G-d gives us any more mitzvos”. Ramban says this was more of a “chet” than a “puraniyos”, as punishment was not immediate. Rashi and numerous midrashim note that the passage between the Nuns belongs in Bamidbar, and was moved here in anachronistic fashion to buffer the “puraniyos”.
I see a recurring theme here: when Bnei Yisrael are at their utmost highest, they also seem to simultaneously be at their lowest, or at least, at the potential of “the higher you are, the harder you fall”: witness krias yam suf [“halu ovdei avoda zara, v’halu ovdei avoda zara], matan torah and the egel [so which exactly were they running from? Ma’amad Har Sinai wasn’t exactly an uninterrupted spiritual crescendo.] And now this: three days away from the literal promised land, and a chain of events is sparked that leads to a forty-year delay in the redemption, among other unforeseen negative consequences.
But lets ignore the possibility of the bar being set too high for a moment. [Interestingly, Ramban doesn’t necessarily do that; he reasons that the Nun bracket broke up a chain of three puraniyos, which would have established a chazaka of puraniyos. In other words, G-d’s help ensured that things didn’t get worse.]
Instead, lets see why exactly a mental attitude could have been the first link in the chain that led to the national tragedy that was the first Tisha B’Av, the Chet Hameraglim.
It seems that the attitude toward this “turning away from G-d”, was alas, a nationwide one. Were they “saru meHar Hashem” as “ke-ish echad, ke-lev echad” like they had stood at Matan Torah? While the pluralistic lashon might be viewed as circumstantial, Ramban’s explanation of the double Nun as a Divine buffer to a national puraniyos might lend extra credence to the notion.
Rashi on 11:1, quoting a machlokes in Sifri as to where and who the Fire burned--either the “gerim”, the “erev rav”, or the “gedolim” (”ketzinim”)—might provide a more salient point. It wasn’t just that the attitude of tinok boreach mibeis hasefer was national…it was that it might have been coming from the top all the way down.
We will see in the next two parshiyos that this was unfortunately true.