John Calvin Commentary Exodus 4:29

"And Moses and Aaron went and gathered together all the elders of the children of Israel:" — Exodus 4:29 (ASV)

And Moses and Aaron went. We are here briefly told how faithfully and devoutly the two brothers executed the commands of God. They gather together the elders of the people, because the vast multitude, as we are told they were, could not be assembled in one place. Besides, God did not wish to contend by means of the tumultuous and confused clamor of a mob, but with the miracles, which calmly breathed forth His divine power.

But it is again noteworthy that Aaron is substituted to speak in place of Moses. For if slowness of speech prevented Moses from doing so, why is God’s message not directed to Aaron? Why is there this indirect procedure, where Aaron proclaims to the people not what he himself heard directly from God, but what he received indirectly through his brother, unless it is because this method is pleasing to God for the purpose of testing their faith?

For while this test showed the humility and modesty of Aaron, since he did not object to depend on his brother’s mouth, so also the teachableness of the elders is evident in their acceptance of God's commands being passed to them in this way, from hand to hand, and in not meticulously questioning why God did not address them directly, or thunder from on high. They were,⁶⁴ however, aided by the miracles, because they were so numbed by their miseries that otherwise simple preaching would have had no weight with them.

⁶⁴ “Cependant Dieu ait supplee a leur infirmite par l’aide des miracles;” still God helped their infirmity by the assistance of the miracles. — Fr..