Simply, Hashem told Moshe Rabbeinu, “Enough! Do not continue asking to enter Eretz Yisrael. It is not happening. The decision has been made.” Chazal (Sotah 13) offer an alternative understanding of rav lach: Rav yeish lach — you have a Rav/Rebbe/spiritual guide—Yehoshua. On the surface, Chazal’s exposition is enigmatic. It appears almost as if Hashem was calling attention to the fact that Moshe would not enter Eretz Yisrael – adding that Yehoshua is his Rav. It is not bad enough that Hashem did not accept his pleas to reverse His decree, that he had to be reminded that he was no longer in charge. His faithful student, Yehoshua, was now the Rav.
In his preface to Teshuvos Nesivos Ohr, Horav Yaakov Nota, zl (Dayan in Kletzk), writes that, on the contrary, these words were meant to sooth and assuage Moshe’s feelings. True, he personally was not destined to enter the Land, but the fact that his prize student was taking his place, carrying on his legacy, should comfort him. “Moshe, you should know that every positive action that Klal Yisrael performs once they enter the Land will be added to your Heavenly account, as if you personally had performed the mitzvos.” When a great Rebbe leaves this world, but leaves a faithful student to teach, lead and carry on his legacy, the loss is real; yet, the people are never truly left bereft. Yehoshua was Moshe’s successor in more than position; he was the embodiment of his Rebbe – if that could be possible. Yehoshua’s greatest merit was his uncompromising fidelity to his Rebbe – not in slavish imitation, but in living continuity. Moshe’s legacy remains ever-present, undiminished by the veil of death, for each time his student teaches, shows care, inspires – Moshe’s legacy becomes a living entity.
