After Ishmael’s wife, and a daughter, and a son, had plead for Nephi, Laman and Lemuel desist. At least for a time, they are repentant. They ask, and receive, Nephi’s forgiveness. Nephi continues to assert his divine mandate, and therefore suggests that they should also seek Jehovah’s forgiveness.
Nephi wrote this story to provide further evidence of his changing position within the family. Once it is over, he wraps it up quickly. We do not get the same description of repentant Laman and Lemuel as we do the rebellious Laman and Lemuel. That isn’t the reason for writing.
At the end of verse 21, Nephi signals that he has finished with this substory because they “did again travel on our journey towards the tent of our father.” When they arrive, “they did give thanks unto the Lord their God; and they did offer sacrifice and burnt offerings unto him.”
As with the previous occasion, it is easily understandable that they make a thanks offering. The burnt offering was the more serious, and probably occasioned by the temporarily murderous intent of Laman and Lemuel.