bamidbar

The Posuk says מבן עשרים שנה ומעלה כל יצא צבא.. תפקדו אתם
The Ramban says the reason it says a Loshon of פקידה is because the Jews weren't supposed to be counted by head, but rather by each person giving a half shekel. In that way, we'll know how many people there are. In the time of Dovid Hamelech, 70,000 people died from a magaifa even though he also counted them by taking something.
The Ramban says that happened because he counted them for no reason.
R' Ruderman asks, if Dovid Hamelech sinned why are the people being punished?
The posuk says that the Levi'im were not counted with the rest of the people.
Rashi says one of the reasons was that there was going to be a gezaira on all those that were counted from 20 years & up, that they were going to die in the midbar. Hashem said "I don't want this shevet included in the decree for they're mine, they didn't sin with the eigle". It's apparent from the medrash that had the bnei levi been counted with the rest of the people, they too would have been punished, even though they didn't sin.
R' Chaim Shmulevitz says that from here we see the way Hashem runs the world. If there is a decree on the public, even people who are undeserving of any punishment will still get punished for they're part of the כלל. Therefore, the Torah said not to count them together with everyone else for once they're in the כלל then there's no escaping punishment. R' Chaim continues, if this is how it is for something bad, how much more so for something good. If you're part of the כלל when Hashem's giving beracha, then even if you're not deserving you'll still merit the beracha. But if you separate yourself from the כלל, then you'll lose out on the berochos. We saw this when the Mir yeshiva was saved from the Nazis. Whoever wasn't there at those vital moments wasn't saved together with the yeshiva.
Similarly says Rav Ruderman, when Dovid counted the people he took them out of the כלל & each person was on his own to be judged separately. When one is judged on his own, it's next to impossible to come out unscathed, hence the magaifa. Rabbainu Bichaya says when we're all judged together, we're saved because of the zechus of the כלל, teaching us that we have to always be part of the כלל. We shouldn't think we know better & do our own thing but always to be a part of כלל ישראל!