Midrash for Exodus 12:1

“And Hashem said to Moses and to Aaron in the land of Egypt, saying, ‘I hear that the the word was to Aaron and to Moses. When it says, ‘It happens on the day Hashem spoke to Moses (in the land of Egypt)’ (Exodus 6) - it was to Moses and not to Aaron. If so why does it teach, ’to Moses and to Aaron'? Except it teaches that just as that Moses was crowned for leadership, thus also Aaron was crowned for leadership. For what reason did he not speak with him? Because of his respect for Moses. Aaron is found excluded from all of the leadership that is in the Torah except from three places, from which it is possible.

...R’ Yehoshua be Levi said: If the nations of the world knew how good the Holy Temple was for them, they would surround it with fortifications in order to guard it. It was better for them than it was for Israel, just as Shlomo ordered his prayer “And also to the stranger, who is not of Your people Israel…” (Kings I 8:41 and it is written “…and do according to all that the stranger calls You for…” (Kings I 8:43) But when it comes to Israel, what is written? “…and give to each man according to his ways, whose heart You know…” (Chronicles II 6:30) If it was appropriate, He would give, and if not He would not. Don’t say that (they should value) the Holy Temple. Rather, if it were not for Israel the rain would not fall and the sun would not shine, because in their merit the Holy One brings plenty to His world. In the world to come the nations of the world will see how the Holy One is with Israel and they will come to cleave to them, as it says “In those days, when ten men of all the languages of the nations…” (Zechariah 8:23)

1) "And He called to Moses and the L–rd spoke to him, etc." "to him" — to exclude Aaron. R. Yehudah b. Betheira said: Thirteen dibroth (accompanied by a command) were stated in the Torah to Moses and Aaron, and, corresponding to them, thirteen limitations, to teach us that they were not spoken to Aaron, but to Moses, to tell them to Aaron. (The dibroth: 1) [Shemoth 6:13]; 2) [Shemoth 7:8]; 3) [Shemoth 9:8]; 4) [Shemoth 12:1]; 5) [Shemoth 12:43]; 6) [Vayikra 11:1]; 7) [Vayikra 13:1]; 8) [Vayikra 14:33]; 9 [Vayikra 15:1]; 10 [Bamidbar 2:1]; 11 [Bamidbar 4:1]; 12 [Bamidbar 4:18]; 13) [Bamidbar 19:2].)