The original rules of the OT were laid out specifically so that the Jews could survive through the desert. Once they found their new home, many of the rules of the desert did not apply anymore. Some of them would still apply though. For instance, eating pork is still not good for you because they have a very dirty kind of meat. Whenever they eat something toxic, it stays in the meat, which we then consume. That's why God told them not to eat pork. He also gave the Jews rules of hygene. At the times of the bubonic plague, the Jews were the only ones that were surviving in great numbers. That's because they followed the hygene rules God sent to them. Once people realized that those rules are important, they were more broadly incoporated in our societies. That's when sanitation was born.
I hope I have educated you.