Albert Barnes Commentary Exodus 4:16

"And he shall be thy spokesman unto the people; and it shall come to pass, that he shall be to thee a mouth, and thou shalt be to him as God." — Exodus 4:16 (ASV)

Instead of a mouth - We may bear in mind Aaron’s unbroken habit of speaking Hebrew and his probable familiarity with Egyptian.

Instead of God - The word “God” is used of persons who represent the Deity, as kings or judges, and it is understood in this sense here: “You shall be to him a master.”