Narrative analysis: So hard are the hearts of Laman and Lemuel that the power of Nephi's forgiving message is lost on them, and they hear only the accusations. Those accusations probably touch a sufficiently familiar cord that Laman and Lemuel are embarrassed by their truthfulness, but the reminder is painful. To remove their pain they do not repent, but rather project their anger once again toward Nephi to attempt to remove their source of pain by killing him.
Historical analysis: This passage has been used to provide topographical data about Bountiful. If Laman and Lemuel were going to throw Nephi into the depths of the sea, the logical conclusion is that they were near a cliff that fell away into the ocean. Had they been standing on a beach, the threat to throw Nephi into the water would have been shallow indeed.