Following the disastrous plague caused by the actions of the Midianites, an army of Klal Yisrael was formed to wage war and take revenge. Rashi notes that the grammatical structure of the words in the passuk reveals that no one actually wanted to go to war — and so they were forced into it. Rashi also quotes the Midrash which explains that Bnei Yisrael knew that once revenge was taken, Moshe Rabbeinu would pass away. As they didn’t want to lose their leader, they were reluctant to do anything that would bring his death closer.
The Midrash notes how different this behavior was from what had transpired just a short while earlier, when the Jews had been loudly and vociferously complaining to Moshe, to the extent that he was worried he would be stoned. How could their feelings have changed so completely in such a short span of time?
The Shelah Hakadosh explains that sometimes, complaints against a leader are due to bad character traits which cause people to complain and be ungrateful. At other times, however, they result from people feeling so close to the leader that they are comfortable enough to openly express their feelings, without holding back as one normally would with a revered authority figure. Since the Torah tells us that the Jews were distraught at the idea that Moshe Rabbeinu was about to pass away, we know that their complaints were due to a sense of closeness — Moshe was almost like a father to them.
In our own lives, we tend to be far more openly critical of those close to us. This is generally not because we dislike them, but because we feel more comfortable to express our feelings. Within measure, this can be a good sign, as long as we express ourselves with respect. However, feeling overly comfortable with others can lead us to behave in ways that are frankly unacceptable, simply because we can get away with it.
It's also important to be aware of the flipside of this observation. When people close to us are too critical for our liking, we can give them the benefit of the doubt and remember that their feelings may be coming across too strongly only because they feel so close and comfortable with us.
