John Calvin Commentary Exodus 4:6

"And Jehovah said furthermore unto him, Put now thy hand into thy bosom. And he put his hand into his bosom: and when he took it out, behold, his hand was leprous, as [white as] snow." — Exodus 4:6 (ASV)

Put now thy hand into thy bosom. By this sign Moses was instructed that what is in the greatest vigor withers away at once, at the command of God, and that what is dry is thus restored to its original vigor. In a word, the statement of Paul was confirmed by it, that God calleth those things which be not, as though they were (Romans 4:17).

It was, so to speak, a kind of leprosy when Moses was banished from the court into the land of Midian, where he led his flock through wild and rough places, among thorns and brambles. After he had passed forty years like one half-dead, having no dignity or name, he regained, as by a restoration (postliminio), what he had lost. Therefore God now promises him that He would soon restore what He had taken away.

This is the simple connection of the sign with its effect, with which sober readers will be content, without giving heed to the subtleties of others. For this was particularly necessary to be understood: that all men stand or fall according to God’s will; that when they seem most strong, their strength suddenly fails, and they waste away; and, again, as soon as God pleases, they return from their deformed and failing state to vigor and beauty.

In this way the holy man learned that, as he had lain in obscurity for a time because he had been withdrawn by God’s hand from the society of men and had been cast into solitude, so he need not despair of becoming a different man by the same hand.

This condition, too, in some measure, pertained to the whole body of the people. However, because it better suits the person of Moses, it is preferable to retain this exposition, so that, considering only his present position as a lowly and humble shepherd, he would not distrust his capacity for undertaking his office, but would rather expect dignity and boldness to be given to him by God.

Moreover, God did not mean to instruct Moses individually only (as we have said) but also to raise him above the contempt of the people. This was so that the exile, by which his dignity had been marred, would not detract from his influence and authority; but rather, because the calling of God shone forth in him like a resurrection, he would, at the same time, be invested with weight and reputation.