John Calvin Commentary Exodus 17:5

"And Jehovah said unto Moses, Pass on before the people, and take with thee of the elders of Israel; and they rod, wherewith thou smotest the river, take in thy hand, and go." — Exodus 17:5 (ASV)

And the Lord said to Moses. God commands him to go out into their midst, as if He would expose him to the danger of immediate death. However, because Moses is persuaded that it is in God's power to calm the fierce passions of men, as well as the waves and storms of the sea, he neither trembles nor retreats.

In this way, God magnified His power, so as to brand them with ignominy while He restrained the people from their previous rebellious stance. In fact, Moses passes before them all, but he only takes the elders with him, in whose presence he is to bring water from the rock, so that they may be eyewitnesses of the miracle.

This middle course, while it does not permit the glory of God’s bounty to be obscured, still shows the multitude that they are unworthy of being allowed to behold His power.

To remind Moses that his rod would not be ineffective, God recalls to his memory what he had already experienced. Yet God does not recount all the miracles; He only mentions what was seen at first: that by the rod’s touch, the waters of the Nile were turned into blood.

God’s declaration that He will stand upon the rock is intended to remove all hesitation, so that Moses would not be anxious or doubtful about the outcome; for otherwise, striking the rock would be futile and illusory.

Moses, therefore, is encouraged to be confident, since God, whom he follows in the obedience of faith, will display His power through Moses’s hand, so that he would undertake nothing in vain or without effect. Meanwhile, although God employs the actions of His servant, He still claims for Himself the honor of the work.