It was Moshe Rabbeinu himself beginning his final charge to the generation whom he nurtured and he correctly suspected that his children were not quite ready to listen. According to the medrash, as Moshe recalls debacles and setbacks his people openly question that perhaps his advanced age was finally catching up with their leader. Sadly enough it is expecting their skepticism that Moshe, according to Rashi, had waited saving these words for the end. Thus Moshe would be spared the aggravation of seeing himself ignored and avoid the attendant embarrassment. Rashi further tells us that Moshe wants all his people gathered together to eliminate any "if only I had been there" challengers, that he is sure there would be.
As disappointing as this may sound, especially of our fathers who merited to see the miracles of Yehoshua, I can understand them quite well. After all, they may have honestly felt that Moshe's litany of failures did not speak to them at all. Why should this generation, eager to enter Israel and too young to have a significant role in the sin of the meraglim or the chet ha'egel or even ba'al peor, have to hear about the sins of the past?
It is precisely this sentiment that Yirmiyahu apparently fears and therefore addresses in one of the closing pesukim of Eicha (5,7): "Our fathers sinned and are no longer and we suffer their sins. (see Targum)". Yirmiyahu has the "next" generation understanding that they are not suffering the punishment thrust upon them, rather they are suffering i.e. tolerating the elders' failures and flaws. In contemporary terms, we and those before us may not have created the divisiveness that brought down the second Beis Hamikdash but we certainly have not found the formula for national harmony.
Similarly Moshe realized that later generations would fall prey to the same lapses and errors and thus found it appropriate to recall these difficult events. Unfortunately we learn that the energies to conquer all of our G-d given land did peter out during Yehushua's time. Ultimately they did make peace with sharing the land with the native pagans and are censured for that. True they were too young to shoulder any responsibility for the chet hameraglim, yet they - as we too - must be wary that our love for our land never lose its depth or the profound passion that it deserves. Furthermore, those gathered to listen to Moshe may have never complained about the manna, yet all future generations should be concerned to be fully appreciative of Hashem's blessings and the obligations that they entail. Finally, Moshe refers to the sin of the golden calf as the sin of "enough gold" to raise in our minds that though we did not smelt golden images we may at times suffer from the complacency that comes with comfort.
In Moshe's words as well, I think we can find how he responds to his children who would rather not hear him out. Looking carefully at the parsha we note that Moshe closes his critical description of the sin of the spies with a seeming incomplete pasuk: "(2,16) And it was when all the men of military age died from amongst the nation." Why does the Torah give this thought an entire pasuk and thus close an episode whereas we would expect it as an introduction to a new parsha?
It would seem to me that the point of this pasuk is simply to put that moment into historical perspective. That the nation fated to die in the desert had passed on was well known, and yet keeping it in mind creates an attitude that gives singular direction. Moshe in this one pasuk gives the most disturbing and energizing tochecha possible. How can one not be inspired knowing that one is being granted opportunities that eluded those who came before? Clearly a generation that approaches the conquest of Israel understanding that this opportunity has been denied to their parents will focus on Israel with unprecedented strength. Thus Moshe Rabbeinu begs his children to study the foibles of the past so that they will internalize the opportunities and responsibilities that lay ahead.
Thus this unfinished pasuk is not a hanging thought, but rather a pregnant phrase waiting for the next generation to write its conclusion.