Nephi gives us the words he spoke to Laman and Lemuel. He shows them by his own brand of logic that since the Lord had commanded him to build a ship, that he would build it. Perhaps Nephi thought that it was this explanation that would appease Laman and Lemuel. It is unlikely, however, that it was Nephi's words that impressed Laman and Lemuel, for they had heard a masterful discourse, and found a way to be angry with it rather than repentant.
The change in Laman and Lemuel is undoubtedly due to their fear of the power of the Lord manifest through Nephi. While they were unable to feel his words, the undeniable power of the spirit in him when he commands them not to touch him clearly affected them, and they obeyed that fear. While their hearts were past feeling, they were still able to feel when hit with a spiritual sledge hammer.