And Moses was learned in all the wisdom of the Egyptians, and was mighty in words and in deeds.
Moses was not an eloquent speaker. He was "slow of speech, and of a slow tongue."
And Moses said unto the LORD, O my LORD, I am not eloquent, neither heretofore, nor
since thou hast spoken unto thy servant: but I am slow of speech, and of a slow tongue.
Not even the Isrealites would listen to him. He had "uncircumcised lips."
And Moses spake before the LORD, saying, Behold, the children of Israel have not
hearkened unto me; how then shall Pharaoh hear me, who am of uncircumcised lips?
And Moses said before the LORD, Behold, I am of uncircumcised lips, and how shall
Pharaoh hearken unto me? Exodus 6:30
So God made Aaron his spokesman instead of Moses.
The anger of the LORD was kindled against Moses, and he said, Is not Aaron the Levite thy brother? I know that he can speak well.
... And thou shalt speak unto him, and
put words in his mouth: and I will be with thy mouth, and with his mouth, and will teach you what ye shall do. 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. Exodus 4:14-16