"Indeed, Pharaoh exalted himself in the land," meaning he transgressed, "and made its people into factions," meaning into sects. "He oppressed a group among them, slaughtering their sons and keeping their women alive," meaning the Children of Israel who were in Egypt under the power of Pharaoh. The group whose sons he would slaughter [are the males], and the group whose women he would keep alive [are the females], and this is what Pharaoh used to do.