What did Aaron speak to the elders of Israel when he and Moses gathered them together?
When Moses and Aaron gathered the elders of Israel, Aaron spoke all the words that the Lord had spoken to Moses. He served as Moses' mouthpiece, delivering God's message to the assembled elders, while Moses was the one through whom God gave the direction.
Les explains that Moses and Aaron were joined together because Moses had complained he could not speak, so God said Aaron would be his mouthpiece. Aaron thus became the spokesman, but Moses was the one through whom God did the speaking and gave direction. They approached the children of Israel in Goshen, and according to Exodus 4:29, Moses and Aaron gathered all the elders of Israel. Aaron then spoke all the words which the Lord had spoken unto Moses. Les points out the order: God spoke to Moses, and Aaron delivered those words to the elders.
And Moses and Aaron went and gathered together all the elders of the children of Israel: