“יֵאָסֵף אַהֲרֹן אֶל עַמָּיו כִּי לֹא יָבֹא אֶל הָאָרֶץ אֲשֶׁר נָתַתִּי לִבְנֵי יִשְׂרָאֵל עַל אֲשֶׁר מְרִיתֶם אֶת פִּי לְמֵי מְרִיבָה”
“Aaron will be gathered to his people; for he shall not enter the land which I have given to the sons of Israel, because you rebelled against My command at the waters of Meribah.”
God tells Moses and Aaron that Aaron will be ‘gathered’ to his people. We learn here that God reveals the time of death for the Tzadikim. The passing of Aaron is defined as ‘gathered’. The commentator Rabbi Meir Leibush (1809-1879 מלבי”ם) explains that Aaron didn’t go through the regular process of death but his soul left the body as a person undresses himself from clothing. Aaron soul was also connected to the Tzadikim in heaven and his body stayed ready for the Resurrection.
“וְשַׁבֵּחַ אֲנִי אֶת הַמֵּתִים שֶׁכְּבָר מֵתוּ מִן הַחַיִּים אֲשֶׁר הֵמָּה חַיִּים עֲדֶנָה”
“So I congratulated the dead who are already dead more than the living who are still living.”
The Zohar quotes this verse to praise those who went through the process of death and reincarnation. They are better than those who are in this world for the first time. With each reincarnation we make corrections (easy or hard) that progress us and make the next reincarnation an easier process.
Even though Aaron was pure in his actions he still needed to correct his part in the sin of the Golden Calf and reincarnate again. He reincarnated om Eli the priest, (1 Samuel 4:17,18). Eli’s two sons killed when they lost the Holy Ark to the Philistine. When Eli heard the message he fell and broke his neck (correction for separation from the upper levels)).