Commentary for Deuteronomy 31:28

הקהילו אלי ASSEMBLE UNTO ME [ALL THE ELDERS OF YOUR TRIBE] — They did not, however, blow the trumpets that day to call the congregation together (as is prescribed in Numbers 10:3), because it states (Numbers 10:2) “Make for thee [two trumpets of silver]” (which Rashi explains to mean that no one should use them except himself), and he had not empowered Joshua to use them. Indeed they were hidden away even during his (Moses) lifetime — on the day of his death, thus fulfilling the words of the text, (Ecclesiastes 8:8) “There is no authority on the day of death” (cf. Midrash Tanchuma, Vayechi 2 on ויחי and ‎Midrash Tanchuma, Beha'alotcha 10 on בהעלתך).‎

ואדברה באזניהם את הדברים האלה, the words of poetry contained in the portion Haazinu.

הקהילו אלי, “Assemble to me, etc.” According to Tanchuma Vayechi 2, on this day Moses did not blow in the trumpets to assemble the people (elders) as was customary, and as Moses had been commanded to do in Numbers 10,2. The trumpets were for the exclusive use of Moses; they were never used by Joshua, but buried during the lifetime of Moses. This was in order to fulfill the statement of Kohelet 8,5 that on the day of one’s death one does not have authority. Seeing this was the day Moses was to die, he did not employ symbols of his authority. Blowing the shofar or the trumpets was a symbol of the authority wielded by the one who blew them or had them blown.