Moses always maintained a position of being “for” his people. He was one of them, a Hebrew. They were God’s covenant people and Moses would not abandon them.
Though he fled from Egypt after killing the Egyptian, he was not presumptuous to think he was permitted to leave the covenant community altogether. He was part of it even while in Midian.
And that older covenant community had elders in its midst. Moses recognized them. God recognized them too. They were important leaders of the community. They represented the community before God and mankind. This is consistent with the newer covenant community (or church) as well.
So, as God announces His rescue mission to Moses, He involves the elders in the mission:
16Go and gather the elders of Israel together and say to them, ‘The LORD, the God of your fathers, the God of Abraham, of Isaac, and of Jacob, has appeared to me, saying, “I have observed you and what has been done to you in Egypt, 17and I promise that I will bring you up out of the affliction of Egypt to the land of the Canaanites, the Hittites, the Amorites, the Perizzites, the Hivites, and the Jebusites, a land flowing with milk and honey.”’ 18And they will listen to your voice, and you and the elders of Israel shall go to the king of Egypt and say to him, ‘The LORD, the God of the Hebrews, has met with us; and now, please let us go a three days’ journey into the wilderness, that we may sacrifice to the LORD our God.’1
The bible does not tell us how these men became elders. They just exist. They show up as part of the narrative and are recognized as integral to the Hebrew community.
Moses would go and speak to them. He would tell them of God’s plan. They would need to accompany him and seek permission from the king of Egypt for the people to travel out of the land to worship God.
The elders were representatives. Somehow they came to be from within the community and were given authority to speak for the community. God acknowledged them; Moses acknowledged them; the people acknowledged them; and Pharaoh acknowledged them.
How did they become elders? From where did they come? Furthermore, has there ever existed a nation or people that did not have elders?
Exodus 3.