Strange Things Jews Do and Why

Not eating pork, shellfish, etc.

Lev. 11: You may eat any animal that has a split hoof completely divided and that chews the cud.... Of all the creatures living in the water of the seas and the streams, you may eat any that have fins and scales.... These are the birds you are to detest and not eat...

What about “non-kosher” beef, etc?

Deut. 14: You shall not eat anything which dies of itself.

Ex. 22: You shall be holy men to Me, therefore you shall not eat any flesh torn to pieces in the field; you shall throw it to the dogs.

From these and other verses, the Rabbis infer that in order to be fit to eat (and kosher does mean “fit, appropriate for a purpose”), an animal (of the proper sort) must be slaughtered, and slaughtered the right way. The Talmud gets very detailed and technical (not for the squeamish!) in discussing exactly how slaughtering must happen, precisely which parts of the animal are forbidden, how to remove the blood from the meat (See Lev. 17), etc. So meat not known to be done just right cannot be considered kosher.

Not eating milk with meat

Ex. 23, Ex. 34, Deut. 14: You shall not boil a young goat in its mother’s milk.

This injunction is repeated three times, from which the Rabbis infer a broader prohibition than just that which is mentioned. There are different traditions regarding how long one must wait after eating meat before one can eat dairy. Also, being meat or dairy (or kosher or non-kosher) is also considered to apply to cooking utensils, which can mess up a dish which would be kosher based strictly on ingredients.

Wearing weird boxes and straps on arm and forehead

Deut. 6: And these words that I command you today shall be on your heart....You shall bind them as a sign on your hand, and they shall be as frontlets between your eyes.

Rabbinic tradition specifies the shape and color, and that “between your eyes” really means on the forehead above the spot between the eyes, and “on your hand” means on the upper arm, and various other details. (See http://www.tefillin.co.il/)

Wearing strange striped shawl

Num. 15: Speak to the children of Israel and tell them to make fringes on the corners of their garments for all their generations...

The obligation is to put fringes on four-cornered garments, and the shawl is thus a special four-cornered garment to allow one to fulfill the commandment. The stripes are decorative, and often blue in commemoration of the “thread of blue” also required by the text. (Most people don't have blue in the fringes anymore, because the precise blue dye required is no longer known—though recent research is changing that in some circles.)

This is also the basis of the smaller 4-cornered fringed garment that is worn usually under the shirt.

Not eating bread on Passover

Ex. 12: ... whoever eats anything leavened from the first day until the seventh day, that person shall be cut off from Israel.

The laws regarding leaven on passover are very stringent, and also apply just to owning it. Jews sell their leaven to a non-Jew before passover, a sale that winds up getting cancelled (but not retroactively) after the holiday.

(Remember, a non-Jew is not considered to be violating the commandment, since he wasn't commanded in the first place. This is not a case of taking advantage of ignorance)

Attaching little boxes (with scrolls inside) to the doorposts

Deut. 6: And these words that I command you today.... You shall write them on the doorposts of your house and on your gates.

Wearing skullcaps (kippah, yarmulke, etc)

(Not a Biblical Commandment)

A Rabbinic custom, based mainly on ordinary dress-codes of the time and place, that one does not go out with a bare head. Became widely followed and important.

All those holidays!

Various; most mentioned in Lev. 23.

Also, Purim and Hanukkah are later additions. Purim’s story (and commandment) can be found in the book of Esther. Hanukkah’s Book of the Maccabees is part of the Apocrypha.

Hanukkah is a minor holiday, and gained its extraordinary popularity due to proximity to Christmas. In addition to the historical events, even the Talmud concedes that it is not a coincidence that we have a candle-lighting holiday at just that time of year, but that there was originally a solstice celebration for God for eight days, established by Adam. (Avoda Zara 8a.)

The Jewish family down the street was building this shack on their backyard, and I heard them last night singing in it. And what's with those funny branches they're carrying around?

Lev. 23:42: Live in booths for seven days

Lev. 23:40: On the first day you are to take the fruit of a beautiful tree, and palm fronds, branches of a thick tree and willows of the brook

It says to live in huts, so we live in huts! The defining feature is determined to be the roofing, which must be unprocessed vegetable matter, so people build the walls out of all kinds of things, and there are pre-fab versions with special bamboo mats for the roof (there are reasons why that doesn't count as “processed”).

In practice, people wind up just eating in the hut, not “living” there full-time. The main obligations are eating and sleeping in it, but most people are lenient on the “sleeping” part, especially in cold climates.

The fruits and branches mentioned are interpreted to mean a citron, a palm branch (that's the long one you see most easily), and branches of myrtle and willow. They're used all through the holiday in commemoration of the Temple, since there they were used all through also, even though the text only specifies the first day. Blessings are recited over them and they are waved around at certain points during prayer.

Why do the holidays always wobble around the calendar and don't stay put?

See comments.

The Jewish calendar is a little complicated. The months need to line up with the phases of the moon (that's what a month is, after all: a cycle of the moon), but the years have to align with the solar year, because Passover is described as being in the spring (Ex. 34, and others). If the year were purely lunar, it would slide around the seasons, as indeed the Islamic calendar does. So there are all these computations, leap-years with an extra month, and so on, to make things like up more or less. The average result is pretty good, but in the short term things slide forward and back a lot relative to the all-solar Gregorian year.

On the Jewish calendar, the holidays do fall out on the same date every year.

Not driving/working/turning on lights/etc on Saturdays

Ex. 20, among others: Six days you shall work and get everything done, but on the seventh day it is Sabbath for the LORD your God; you shall do no work...

Precisely what constitutes “work” is described in fine detail in the Talmud, starting with the 39 main categories of work and working down to the many derived subcategories of them. These are also extended by various stringencies, plus modern interpretations, e.g., that electricity is considered like fire, and therefore is forbidden (See Ex. 35). The categories include many seemingly non-strenuous activities, like writing, sewing, wringing, etc.

Wait, but how come Jews will hire or otherwise engage non-Jews to perform these things for them on Saturdays? Isn't that like hiring someone to sin for you?

This is actually an important point to realize. Judaism is not like Christianity or Islam in that Judaism does not hold that everyone in the world should be Jewish (whereas Christians believe everyone should be Christian and Muslims believe everyone should be Muslim). From the perspective of Judaism, a non-Jew who "violates" Sabbath is not committing any sin at all, because the commandments of Sabbath don't apply to him in the first place. Sabbath was commanded to the Children of Israel, and is not binding on the whole of humanity. There are a small number of laws (seven) which are considered to be binding on everyone (the Seven "Noachide" Laws; see Genesis chapter 9), but not the whole huge compendium of laws.

(This is an interesting topic, worthy of more discussion, but not here.)

All those fast days

Lev. 23 for Yom Kippur; others are non-Biblical

Various days in the year have been declared fast days by the Rabbis through the ages, in commemoration of one tragedy or another. There are even a whole lot more that nobody observes anymore.

Breaking a glass at weddings

(Not a Biblical commandment)

Just a custom, done in memory of the destroyed Temple, to remind us even at the happiest of moments that we still mourn for the loss of the Temple (cf. Ps. 137)—or so goes the standard explanation. It probably had its origins in chasing away demons, like so many other customs involving wanton destruction seem to be, among Jews and non-Jews alike. (There is, however, some Talmudic basis for it, see Berakhot 30b)