Or HaChaim on Numbers 14:29/אור החיים על במדבר י״ד:כ״ט

1 מבן עשרים שנה..אשר הלינותם, "from the age of twenty and up..because you have complained against Me." We must try and understand why G'd said אשר הלינתם. If the word אשר is to be equivalent to על אשר (the way we have translated it), then there is nothing new here. G'd had mentioned this already in verse 27!

2It appears that these words were necessary in view of G'd having spoken of the decree applying to the people who were twenty and over. We might have interpreted this to mean that anyone 20 years of age at the time of the decree was included in the decree that he had to die in the desert. As a result, men who had not been twenty years old at the time of the Exodus would be included in this decree. To make it clear that this was not so, the Torah says אשר הלינתם, people who were 20 years old from the time you started complaining, i.e. immediately after the Exodus. If anyone of the complainants had been twenty years old at the time he complained, he was now included in the group of people to whom this decree applied. This is precisely what G'd had meant when He told Moses in verse 22 that the Israelites had tested Him already ten times.

3Perhaps the generation in question did not notice this nuance of the verse as to who was and who was not included in the decree and they thought that the decree applied only to people who had turned twenty as of that day. As a result of such a faulty interpretation they examined who had died in the fortieth year of their wanderings on the night of the ninth of Av. They found then that not a single one had died on that night. When they checked for the next 5 nights and found that not a single Israelite died during those nights either, they declared the 15th of Av of that year as a day of rejoicing concluding that the decree had come to an end (compare introduction to Midrash Eycha Rabbah.) It is difficult to understand why they should have expected anyone to die during the night of the ninth of Av in that year unless they had misunderstood the meaning of who was included in the description "from twenty years and over."

4Possibly, G'd had couched the decree in a language which permitted more than one interpretation, something G'd is fond of doing on occasion. The reason G'd couches something in ambivalent language is to allow for a more lenient interpretation if the people deserve it, or for a more stringent interpretation in the event the people do not deserve it. A classic example of what I have in mind is Genesis 2,17 where G'd warned man not to eat from the tree of knowledge on pain of death. The "death" warning is phrased as follows: "for on the day you eat from it you will surely die." This could be taken to mean that death would be practically instantaneous, i.e. the very same day, or it could be taken to mean that on that day man would become mortal but that death might still be a long way off and that the "day" G'd spoke of was the amount of time He considered a "day" in His calendar, i.e. 1000 years in our time. If Adam would repent, G'd would apply the latter interpretation, if not, He would let Adam die within 24 hours after he had eaten from the fruit of that tree. In our verse G'd also used ambivalent language when the Torah wrote אשר הלינתם. The expression lends itself to two interpretations. 1) על אשר הלינותם, "because you have complained." 2) "from the time you have started to complain the first time," as we explained earlier. G'd meant that if the Israelites would repent and behave from now on He would apply the more lenient of the two interpretations, i.e. only people who had reached the age of twenty before the episode of the spies would die. If the people would become guilty of further misdemeanours, G'd would consider all those who had been twenty years at the time of the first complaint as included in this decree. When G'd had mentioned that the Israelites had tested Him ten times, He referred to the majority of the complainers. When the people realised on the night of the ninth of Av in the fortieth year that no one had died, they celebrated as the decree had finally been lifted from those who had left Egypt while under twenty years of age but had been 20 years of age when the decree was pronounced.