The book of Ether originates in a very different time of human history than did Lehi and Nephi. One must shift gears to understand the world in which they lived. They seem to have left the Middle East shortly after the fall of the tower and the confusion of the languages at Babel, before Abraham and King Hammurabi, and long before Moses. Perhaps about 2300 BC, an arbitrary date that seems to work out based on the underlying royal genealogy. Beginning that long ago, the Jaredites did not know about the Abrahamic Covenant, the Law of Moses or circumcision, nor did they have brass plates to take as Lehi did. There was no national religion; everything was local. They may have known of the prophets Noah and Enoch. They must have had some knowledge of the ancient dealings of God in the history of mankind, because Moroni records that they had an account of the creation (see Ether 1: 4–5).
As far as their other literary sources, we know they kept their king list and probably some kind of oral history, if not a written one, up to the fall of the tower. The twenty-four plates were made after the migration to the promised land. We cannot measure the Jaredite culture against the Nephite culture, because we do not even know for sure that they were Semitic, though some of the names and the root of their creation story may indicate that they were. It is a blessing that they made a record at all.
Were any laws recorded on those plates of Ether? Hammurabi (ca. 1810–1750 BC) was the sixth king of the First Babylonian dynasty of the Amorite tribe, reigning from c. 1792 BC to c. 1750 BC, is best known for having issued the Code of Hammurabi, which he claimed to have received from Shamash, the Babylonian god of justice. Hammurabi was eventually able to establish a unified Kingdom in the area from which Jared and his brother had earlier originated, when he united Southern and Northern Mesopotamia—the Sumerian culture in the south, and the Akkadian culture in the north. He established a law code, though he was not the first one to do that. Starting a couple hundred years earlier, people began writing laws down and following them. But, before then, as far as we know, there was not much in the way of law. Lehi and his family took with them in 600 BC a whole set of laws, the Law of Moses on the brass plates and a whole culture with them; but which the Jaredites much earlier did not have.
Since they knew of the Creation, they probably knew of Noah. In terms of law, God had made a covenant with Noah that related especially to protecting life and avoiding murder—if a person killed another man, the perpetrator’s blood had to be shed (Genesis 9:6). These rules issued by Noah are thought to apply to all of Noah’s posterity as the minimal rules of basic civilization. These very fundamental things are what we ever see by way of legal regulation in the Book of Ether. We see other atrocious things that apparently were considered “legal” within their civilization.