The end of Moshe's mission

Parshas Vayelech begins with Moshe telling Bnay Yisrael that he will not be leading them into their homeland. 31:2  I can no longer go or come לֹא אוּכַל עוֹד לָצֵאת וְלָבוֹא
Rashi explains that can here is used in the sense of may, not to signify a lack of ability but a lack of permission 

וילך משה וגו', לא אוכל עוד לצאת ולבא: יכול שתשש כחו, תלמוד לומר (דברים לד, ז) לא כהתה עינו ולא נס לחה. אלא מהו לא אוכל, איני רשאי שנטלה ממני הרשות ונתנה ליהושע:

Moses went…I can no longer go or come: One might think [this means] that Moses’ strength had ebbed [and that is why he could no longer go or come]. Scripture [however] states [regarding Moses], “His eye had not dimmed, nor had he lost his [natural] moisture” (Deut. 34:7) [which teaches us that his powers were intact even on his last day of life]. What then is [the meaning of] “I can no longer?” “I am not permitted,” because authority was taken from him and granted to Joshua.

My grandfather looks at the rest of the verse for the explanation of this sense. 
 G-d told Moshe that he will not cross the Jordan River. אָמַר אֵלַי לֹא תַעֲבֹר אֶת הַיַּרְדֵּן הַזֶּה:
Once Hashem had so decreed, the flow of wisdom [needed to lead them] ceased. That fits with what our Sages said in Brachos 32a:    אמר רבי אלעזר אמר לו הקדוש ב"ה למשה
משה רד מגדולתך"
"כלום נתתי לך גדולה אלא בשביל ישראל ועכשיו ישראל חטאו אתה למה לי
מיד תשש כחו של משה ולא היה לו כח לדברWhat means "Go, get thee down" ? 

R, Eleazar said : The Holy One, blessed be He, saidto Moshe, 

"Moses, descend from you greatness. 

Have I not given you greatness only for the sake of Israel? And now that Israel has sinned, what are you to Me?" 

Immediately the strength of Moshe weakened, and he had not the power to speak.

Related post: http://kallahmagazine.blogspot.com/2015/10/dvar-yehudah-parsha-points-from-my.html