Chasidut zu Dewarim 31:27

The prayer of Moshe our teacher peace be upon him to enter the land and was not answered positively. It seems that it was to elevate all the prayers of the Children of Israel that weren't able [the prayers] to go up. All those ineffective prayers had a fixing needed, and this happened through this prayer. And it was all with a certain measure, since Moshe our teacher peace be upon him sacrificed his life for the Children of Israel and even this request of going up to the Land of Israel was also only for the goodness of the Children of Israel. Because he knew that if those prayers did not make it in, the Children of Israel would destroy their own ways, as it is written "if while I am still living etc" (Deut. 31:27). Therefore, this prayer was helpful to the Children of Israel, even if his request was not responded positively, the prayer was not for nothing, God forbid.