My grandma is an adventist and she couldn't eat pig, rabbit most sea food and a few more. In all honesty, those are quite stupid rules, you either meat or you don't, those seemingly random chosen animals make no sense to me. That's why I can't take the bible seriously. Not even believers of the bible come to an agreement, you have christians, adventists, orthodox and many more.
There are two issues here that are worth exploring.
1) Can costly ritual create purpose in and of itself?
Ritual requires sacrifice of material, time, or behavioral modification. Participating in ritual does several things. First it reinforces to the participant that he or she is serious about his belief structure. One paying only lip service to a concept would not undertake a hardship in its service especially if he did not fully understand the reason for the hardship.
Aesop's Fables were colllected and written 620 and 564 BC. One of the most famous is the story of the farmer and the viper. We know the story is at least 2500 years old and as an oral story it could be far older. The story concerns a farmer who finds a viper freezing in the snow. Taking pity on it, he picks it up and places it within his coat. The viper, revived by the warmth, bites his rescuer. The farmer dies reproaching himself "for pitying a scoundrel,".
One of the transformative elements of religion is the fostering of reciprocal altruism among strangers. Do unto others as you would have them do unto you. This principle if widely adhered to is fundamentally transformative. The world, however, is full of vipers and behaving altruistically with a viper is dangerous at best. It is not advisable for example to take a homeless person into your home to help him "get back in his feet" until you learn quite a bit more about him and the reasons for his homelessness.
So how do we determine who is a viper and who is not. If we are serious about the principle of mutual altruistic reciprocity we have to make this determination. One of the most powerful ways is to determine if the individual in question has committed themselves to a set of known core beliefs. It is very easy for a sociopath to lie. It is incredibly difficult for a sociopath to participate in costly rituals expressing allegiance to concepts they distain especially over prolonged periods of time.
Participation in voluntary ritual thus serves not only to reinforce internal commitment but also as external signaling informing others who you are. It's not a perfect source of information but actions always speak louder then words.
2) Is it possible that the Bible could be true but our understanding is simply lacking or our interpretation overly simplified?
This at least warrants consideration. Humans have a general tendency towards arrogance unwarranted extrapolation and overstating both our knowledge of the world and the reliability of that knowledge.
In recent years there has been a growing body of data indicating that eating pork might be actually unhealthy and we are better off with alternative sources of meat. I am unaware of similar data on shellfish or if it has been studied.
See:
https://bitcointalksearch.org/topic/m.17257930For these reasons I don't think we can conclude that these rules and rituals are stupid. At most we can say that we do not understand their purpose and question their value.