With a stretched out arm - The figure is common and quite intelligible; it may have struck Moses and the people the more forcibly since they were familiar with the hieroglyphic which represents might by two outstretched arms.
Related Commentaries of Exodus 6:6
Exodus 6:6
6 Wherefore say unto the children of Israel, I am the LORD, and I will bring you out from under the burdens of the Egyptians, and I will rid you out of their bondage, and I will redeem you with a stretched out arm, and with great judgments: