אַתָּ֣ה תְדַבֵּ֔ר אֵ֖ת כָּל־אֲשֶׁ֣ר אֲצַוֶּ֑ךָּ וְאַהֲרֹ֤ן אָחִ֙יךָ֙ יְדַבֵּ֣ר אֶל־פַּרְעֹ֔ה וְשִׁלַּ֥ח אֶת־בְּנֵֽי־יִשְׂרָאֵ֖ל מֵאַרְצֽוֹ׃
Tú dirás todas las cosas que yo te mandaré, y Aarón tu hermano hablará á Faraón, para que deje ir de su tierra á los hijos de Israel.
Rashi on Exodus
אתה תדבר THOU SHALT SPEAK once, every separate message just as you have heard it from My mouth, and your brother Aaron shall express it in eloquent language and explain it in Pharaoh’s hearing.
Rashbam on Exodus
ושלח, he should tell Aaron to tell Pharaoh to let the Israelites go.
Siftei Chakhamim
As you heard it from Me. . . Rashi is explaining why it says, “All that I command you.” You (Moshe) will say each statement before Pharaoh, concisely and only once, just as you heard it from Me. And Aharon your brother will express each statement a few times, eloquently, until it is palatable to the ears of Pharaoh. (Maharshal)