John Gill Commentary Exodus 4:7

"And he said, Put thy hand into thy bosom again. (And he put his hand into his bosom again; and when he took it out of his bosom, behold, it was turned again as his [other] flesh.)" — Exodus 4:7 (ASV)

And he said, put your hand into your bosom again With the leprosy on it: and he put his hand into his bosom again, and plucked it out of his bosom ; quickly after he had put it in: and, behold, it was turned again as his other flesh ; it was cured of the leprosy, and recovered its colour, and was as sound as before, and as any other part of his body.

This was a very astonishing miracle, that he should be at once smote with a leprosy; that this should be only in his hand, and not in any other part of his body; and that it should be cured immediately, without the use of any means; and by this miracle Moses, and the Israelites, might be instructed and confirmed in the power of God, that he that could so suddenly inflict such a disease, and so easily cure it, was able to deliver them out of captivity, which was as death; and that however until Moses might be in himself to be a deliverer of the people, signified by his weak and lepous hand, yet being quickened and strengthened by the Lord, would be able to answer to the character; though, after all, the deliverance must be imputed not to his hand and power, but to the mighty hand and power of God.