Biblical Personalities: Aharon: Selections From The Midrash

“Before I arose,” said Moses, “my brother Aaron prophesied to Israel for eighty years.” (Shemot Rabbah 3:16)
Aaron was in Egypt prophesying to Israel that the Holy One, Blessed is He would reddem them. (5:10)

When the Holy One, Blessed is he, said to Moses in Midian, “Go, return to Egypt,” (Exodus 4:19) the utterance split into two voices and took on two aspects. Moses heard in Midian, “Go, return to Egypt,” while Aaron heard, “Go into the wilderness to meet Moses. (5:9)

Had Aaron know that the Holy One, Blessed is He, would write about him, “Behold, he is going forth to meet you, and when he sees you, he will be glad,” (Exodus 4:14) he would have gone out to greet Moses with timbrels and choruses. (Ruth Rabbah 5:6)

Aaron was greater than Moses. Who is greater than Aaron? The Holy One, Blesed is He. Why did He not speak with Aaron? Because Aaron did not have children who would stand in the breach. Had Elazar and Ithamar stood in the breach, Nadab and Abihu would not have sinned. (Avot D’Rabbi Natan 37:12)