Nephi feels he needs to explain why they didn't have hardly any fires during their trek through the wilderness. Modern research has revealed that during this period it was very dangerous to make fires because of the bands of desert raiders who made a living seizing the property of any travelers passing that way.
The Lord therefore promised Lehi and his company to eat their food raw, even their meat would be made sweet for them. But while Nephi says they obeyed the commandment concerning fires in the desert he was now able to make intensely hot fires and fashion the tools he needed to build a ship.