Exodus 7:9

Shew a miracle. It was obvious that should Pharaoh grant them another audience he would require a display of their credentials, to verify their claim to being messengers of the most high God. As long as such a requirement was not made there was no need to perform miracles before him. For this reason they had worked no miracle at their former interview. Now, however, the time had come when their credentials would be demanded, and an express command was given them to exhibit the first sign (see Exodus 4:3, 4).

Take thy rod. This was Moses’ shepherd staff, called also the “rod of God” (Exodus 4:20). According to Exodus 7:15-18, Moses was directed to go before Pharaoh to request that Israel be permitted to leave Egypt, and to announce that he would smite the waters of the Nile with the staff in his hand. From vs. 19 and 20 it is apparent that this miracle was performed by Aaron, who took Moses’ staff and stretched out his hand over the waters of Egypt. The staff that Aaron held over the Nile can therefore have been none other than the staff of Moses, which had been turned into a serpent. There was but the one staff, with which both Moses and Aaron performed miracles (Patriarchs and Prophets, p. 263).