Moshe begins a brief review of all the events that transpired since leaving Egypt. During this review he takes the opportunity to chastise the people for their complaints and actions during the time period in the desert and he implores them to improve their ways and dedication to the service of Hashem as they enter into the Land of Israel.
Moshe waited for this 11th hour moment to give them the mussar, rather than do so all along throughout the 40 years of wandering through the desert.
Rashi tells us a couple of reasons why Moshe waited until now, the last possible moment, as they are on the cusp of entering into the Land and Moshe is about to die:
- So he would not constantly be telling them off - just once at the end.
- after giving someone mussar, the relationship is often then strained. The rebuked will often try to avoid the rebuker, from embarrassment.
If Moshe would have given them mussar all along, they would have thought of him as a pest and would have begun to ignore him. They would also have avoided him whenever possible. He would not have been able to build the nation like that. He wisely led them through the desert and only at the end gave them the mussar, when he knew he would no longer be making them uncomfortable, as he would no longer be with them.
When giving someone mussar, one has to consider whether the time is opportune. Is it really the best time right now, or maybe later it will be even more effective? Will my mussar now be accepted or will it just push him away further?
The only way to succeed in giving mussar is by considering these questions and making sure your mussar is timed properly. That is what Moshe did.