“Throw it on the ground,” said the LORD. So Moses threw it on the ground, and it became a snake, and he ran from it.
It was a very great honour that Moses was called to when God commissioned him to bring Israel out of Egypt; yet he is with difficulty persuaded to accept the commission, and does it at last with great reluctance, which we should rather impute to a humble diffidence of himself and his own sufficiency than to any unbelieving distrust of God and his word and power.
Commenting on Exodus 4:1-9
And he said, cast it on the ground,.... That is, the rod or staff: and he cast it on the ground, and it became a serpent; not in appearance only, but in reality, it was changed into a real living serpent; for God, who is the author of nature, can change the nature of things as he pleases; nor is it to be supposed that...
A serpent - Of what sort we know not, as the word נחש nachash is a general name for serpents, and also means several other things, see Gen 3:1 : but it was either of a kind that he had not seen before, or one that he knew to be dangerous; for it is said, he fled from before it.