The Famous Donkey

"Moshe took his wife and his sons, mounted them upon the [famous] donkey, and he returned to the land of Egypt....Moshe took the staff of G-d in his hand." [Shemos 4:20]

Why was a donkey chosen for Moshe's mission?

Rashi: Moshe mounted his wife and children on a unique donkey. This was the donkey which Avraham himself prepared for the journey to sacrifice his son Yitzchak. And it is the donkey on which Moshiach is going to be revealed on, as the verse states that Moshiach is "a poor man riding on a donkey" [Zechariah 9:9]

Be'er Mayim Chayim: Rashi is troubled why the verse says that he "mounted them upon the donkey" rather than merely "a donkey". Therefore, he concluded that the Torah must be hinting that it is a famous donkey.

Pirkei d'Rabbi Eliezer: This donkey was born to the famous donkey formed on the first Friday of creation, after sunset [see Avos 5:6]. It is the donkey on which Moshe rode when coming to Egypt. And it is the donkey which the son of David (Moshiach) will ride upon.