> I would think most of the Old Testament laws - dietary restrictions, clothing restrictions, circumcision, etc. - are exactly the same. The purpose is simply to maintain a separate identity.
That is certainly a result, and the typical modern perception of those laws. But, from an historical perspective, their roots are quite practical - and practiced by many contemporary groups for exactly the same reasons:
Dietary laws: Pork and some wild game carries Trichinella, a parasite that causes a very painful disease. Shellfish from warm waters carry multiple diseases, both viral and bacterial. draining animals of their blood greatly increased how long they could be kept. Carnivorous (obligatory vs. opportunistic) birds (including robins) carry all sorts of parasites that vegetarian (not vegan) birds do not. The milk/meat connection is one of the few that is very much behavioral, not practical - and that has to do with some of the pagan animal sacrifice rituals of the time.
Circumcision reduces genital infections - no small thing before antibiotics, practical indoor plumbing, and water-poor environments.
As to Clothing: The basic laws are simple—cover the knees, the elbows, and the collarbone, and don't wear anything skintight. Ever been in the Middle East? Even in the winter, the weather is not very forgiving of exposed skin. In the rainy season (and even Saudi has a rainy season), the mosquitoes, while not as bad as those in Alaska, are pretty nasty and very persistent. Skin-tight - not comfortable at 125F in the shade!
The separate identity expectation is common to many religions, not just the big-three. And the various & sundry rules promulgated to that end Mostly (NOT always) have practical roots that have grown into a life of their own rather than being still connected to their first-causes.