Aaron will speak on Moses' behalf
28 When the Lord spoke to Moses in the country of Egypt, 29 he said, ‘I am the Lord. Tell Pharaoh, king of Egypt, everything that I say to you.’ 30 But Moses said, ‘You know that I do not speak well. Pharaoh will not listen to me.’
1 Then the Lord said to Moses, ‘Look, I have made you like God to Pharaoh. Your brother Aaron will speak on your behalf, like your prophet. 2 You must say everything that I command you to say. Your brother Aaron must tell Pharaoh to let the Israelites go out of his country.
7:1A prophet is a person that speaks God's words. Aaron would be like a prophet for Moses. God would speak to Moses and Aaron would tell Moses' message to Pharaoh.
3 But I will make Pharaoh's mind become hard. I will do many miracles in Egypt that show my power. 4 But Pharaoh will still refuse to listen to you. Then I will show my authority and I will punish the Egyptians. I will bring my people, the Israelites, out of Egypt like an army. 5 Then the Egyptians will know that I am the Lord. I will show my great strength in Egypt and I will lead the Israelites out from there.’