Culture: This convoluted statement that the Nephites “could not be governed by the law nor justice” sounds, on first reading, that they were refusing to obey the law. However, Mormon’s final clause clarifies that they could not be governed by law “save it were to their destruction.” He is referring to the corrupted voice of the people that has replaced the righteous Nephi with a representative of the apostate faction. The Nephites are governed by a law that allows them to make choices, and they are now choosing laws contrary to Yahweh’s ways.
To use a modern analogy, the government continues but with a change in political parties. It is completely legal but also completely wrong, since it represents a departure from Nephite religious ideals and the adoption of wickedness. Thus, it will cause their destruction because they have chosen against Yahweh’s law and hence against Yahweh’s protection.