Adam Clarke on Acts 7:23

When he was full forty years old - This was a general tradition among the Jews: "Moses was forty years in Pharaoh's court, forty years in Midian, and forty years he served Israel."

To visit his brethren - Probably on the ground of trying to deliver them from their oppressive bondage. This desire seems to have been early infused into his mind by the Spirit of God; and the effect of this desire to deliver his oppressed countrymen was his refusing to be called the son of Pharaoh's daughter - see Heb 11:24, and thus renouncing all right to the Egyptian crown, choosing rather to endure addiction with the people of God than enjoy the pleasures of sin for a season.