What does Exodus 4:16 mean?

The Lord is sending Aaron, Moses' brother, to act as the public speaker for Moses' mission (Exodus 4:10–15). Despite what movies, cartoons, and art suggest, it was Aaron—not Moses—publicly passing along the words which God gave to Moses.

Here, God describes the role Aaron would play. First, Aaron would speak on behalf of Moses. Since Moses was either a poor speaker (Exodus 4:10) or simply hesitant (Exodus 4:13), it would be Aaron delivering most of the public messages. That would include conversations with Egypt's Pharaoh and the people of Israel. In this way, Moses would act somewhat like God: giving instructions and information to be distributed by someone. The description may also refer to Aaron's reverence and caution that he would not change what Moses said, since the message came from the Lord.

The first practical record of this special relationship is found later in this chapter (Exodus 4:30). "Moses and Aaron" first appear before Pharaoh in the next passage (Exodus 5:1). The command given here is also repeated in Exodus 7:1–2. As with public speaking, sometimes it was Aaron, acting under Moses' instruction, who acted as a conduit for the Lord's power (Exodus 7:19; 8:16). The first plague would take place through Aaron as Moses told him to turn the water of the Nile into blood (Exodus 7:20).