Jamieson, Fausset and Brown on Acts 7:23-27

23-27. In Ac 7:23, 30, 36, the life of Moses is represented as embracing three periods, of forty years each; the Jewish writers say the same; and though this is not expressly stated in the Old Testament, his age at death, one hundred twenty years (De 34:7), agrees with it.

it came into his heart to visit his brethren--his heart yearning with love to them as God's chosen people, and heaving with the consciousness of a divine vocation to set them free.