He will speak to the people for you. He will be your spokesman, and it will be as if you were God to him.
KJV
And he shall be thy spokesman unto the people: and he shall be, [even] he shall be to thee instead of a mouth, and thou shalt be to him instead of God.
ASV
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.