In these two verses Nephi gets to the heart of his point. He begins with the story of Moses and the drawing forth of the live-giving water. Once again the brothers cannot deny this. They must admit that there was a prophet leading the children of Israel, and that the power of God was manifest.
Verse 30 is pointed directly at Laman and Lemuel. Just as the children of Israel murmured against their prophet and leader, so have Laman and Lemuel done. Once again the brothers cannot deny the history, and cannot miss the allusion to their own situation. Nephi's use of this historical fact to highlight the position of his brothers is a wonderful example of a clear warning message with a hopeful side. The children of Israel may have murmured, but all turned out well after their repentance. So too is the hope held before Laman and Lemuel that they might repent, and all will be well. Nephi is not condemning his brothers outright, but calling them to repentance.