1)
For what did He choose Aharon?
1.
Radak: For Shelichus - "v'Aharon Achicha Yihyeh Nevi'echa" (Shemos 7:1).
2.
Malbim: He sent Moshe because he was Eved Hashem; He sent Aharon because He chose Aharon and his seed to be Kohanim to Hashem. Moshe's seed was not chosen for this.
