"I am not a man of words". With this argument, Moshe Rabbeinu refused Hashem's request to lead Am Yisrael out of Egypt. After seven days, Moshe asked Hashem to appoint his brother Aharon instead. Hashem became angry, and Moshe finally acceded to His request (Rashi 4:10).
As a result of Hashem's anger, Moshe who was to be the kohein gadol, lost the position to Aharon (Rashi 4:14). Alternatively, Moshe was destined to lead Am Yisrael into Eretz Yisrael. Because he refused to accept Hashem's mission for seven days, after seven days of prayer his request to enter Eretz Yisrael was denied (Vayikra Rabba 11:6).
The ability to speak, which defines man, requires a combination of the physical organs of speech and the abstract process of thought unique to the human soul (Targum Onkelos, Breishis 2:7). Moshe Rabbeinu's self-described speech handicap can be attributed to a weakness in this combination. Because he was exceedingly spiritual, Moshe was not a man of words (Maharal, Gevuros Hashem, 28).
Nonetheless, Hashem told Moshe, "[go to Egypt.] I shall be with your mouth and teach you [v'horaisicha] what you should say." The Medrash interprets that Hashem would recreate Moshe, as in vatahar, meaning a new conception, thereby removing his speech impediment (Shemos Rabba 3:!5).
The role of a kohein is to sublimate physical offerings into spiritual service. Similarly, life in Eretz Yisrael demands that physical activities, such as planting and fighting wars, be part of a spiritual personality. Moshe Rabbeinu, by his own admission of faulty speech, disqualified himself from serving as a Kohein and leading Am Yisrael in Eretz Yisrael.
Had Moshe accepted his mission earlier, Hashem would have recreated him, thereby perfecting his speech. This new Moshe would have been able to be a kohein and lead Am Yisrael in Eretz Yisrael.
When Hashem accepted Moshe's refusal to be the sole leader to go to Pharoh (3:10), He appointed Aharon to be Moshe's "mouth" (4:16). This partnership represents, in a broader sense, the partnership of individuals devoted exclusively to spiritual activities with those involved with worldly matters.
"Aharon and all the elders of Israel came to eat bread with Yisro before Hashem" (18:12). Moshe did not partake of the meat, rather he was standing and waiting upon them (Rashi). Eating before Hashem represents the combination of the physical and spiritual. This is the mandate of Am Yisrael, as opposed to non-Jews, who can offer only burnt offerings (Menachos 73b). Aharon, the kohein, is especially dedicated to this idea.
Moshe, however, is entirely spiritual. As such, he did not partake of the meal. Nevertheless, his presence was critical. Those involved in worldly matters must maintain a strong connection with those who are devoted exclusively to spiritual activity (Rav C.Y. Goldwicht, Asufat Ma'arachot, Purim 2001 ed., p. 285).
Correspondingly, those who pursue spiritual goals, such as learning Torah full time, must appreciate the indispensable role of supporters of Torah who earn a livelihood. "Behold how good and how pleasant is the dwelling of brothers in unity (Tehillim 133:1). This refers, in particular, to Moshe and Aharon (Krisus 5b).
The menorah, made by Moshe and kindled by Aharon, consisted of seven candles (Bamidbar 8:2-4). The three candles on each side faced the middle ones. The right three symbolize those learning Torah, while the left three represent those earning a livelihood who support those who are learning. It is only with the joint efforts of both groups that Hashem's plan is fulfilled (Sforno).
This legacy of Moshe and Aharon survived the churban, and, as such, is greater than the Beis Hamikdash itself (Rashi 8:2, as explained by Eim Habanim Smeicha p.318, 1983 edition). The Beis Hamikdash was destroyed because of baseless hatred (Yoma 9b), and can only be rebuilt with greater unity within Am Yisrael.
As we read about Moshe and Aharon and the first ge'ula of Am Yisrael, let us strengthen the unity that their brotherhood represents, and thereby hasten the final ge'ula.