What is the rational of Moshe’s requesting that Hashem release His own vow that Moshe should not enter Eretz Yisrael?
Moshe pleaded the principle that once a part of the vow has been accomplished it is as if the whole vow has been completed without fulfilling the balance of the vow (Nedarim 26). HaShem vowed that “they” (Aharon and Moshe should not enter Israel. Thus, the vow was that together they should not enter Israel. Now Moshe pleaded since Aharon has already died and thus “they” can not enter Israel, HaShem should consider the vow completed and Moshe should be allowed to enter Israel.
HaShem responded רב לך . The burden of the “sin” at the Mei Merivah was upon Moshe (majority to you). The Medrash Rabbah (Chukas 9) clearly states that Aharon did not sin (parable to the case of a creditor that comes to seize the property of the debtor and also seizes the property of his neighbor, etc.).
(In the Mesorah of texts we find the word המן (the word “from” proceeded by a Heh) refers to another occasion of punishment to one that did not deserve death but was close to the action. המן העץ the sin of the tree in Gan Eden. The snake was the causation of the “sin” and was obligation punishment but nevertheless, the decree of death also fell on Adam HaRishon and his descendents.)
Thus, HaShem responded to Moshe that the “sin” that caused the decree was mostly from Moshe, so he can not now expect Aharon’s death to release Hashem’s vow regarding the effect to Moshe (to exempt him from punishment) and to allow him to enter the Land.
