Exodus 4:14-16

14Then the Lord became angry with Moses. “All right,” he said. “What about your brother, Aaron the Levite? I know he speaks well. And look! He is on his way to meet you now. He will be delighted to see you.

15Talk to him, and put the words in his mouth. I will be with both of you as you speak, and I will instruct you both in what to do.

16Aaron will be your spokesman to the people. He will be your mouthpiece, and you will stand in the place of God for him, telling him what to say.