A Seemingly Strange Pre-holiday Practice
Some Jewish laws seem irrational at first glance and seem to be rabbinical attempts to evade biblical mandates, but a closer look reveals that the rabbis created laws to aid fellow Jews. Eiruv Tavshilin is an example.
When a Jewish holiday is followed immediately by the Sabbath, current Jewish law allows families to cook on the holiday foods that will be eaten on the holiday, but forbids them to cook foods on the Sabbath itself and on the holiday for the Sabbath. However, while not changing the rule that cooking is generally forbidden on the Sabbath, the law allows Jews to cook on the holiday for the Sabbath if the family performs the ceremony of Eiruv Tavshilin.
This situation raises questions: (1) Why is cooking allowed on holidays but not on Shabbat? (2) Why is it forbidden to cook on the holiday for Shabbat? (3) What gave the rabbis the power to create a process, the Eiruv, to allow cooking on the holiday for Shabbat if without the process the cooking is forbidden? (4) What is the ceremony of Eiruv Tavshilin? (5) Why did the rabbis require Jews to say a blessing for the Eiruv Tavshilin that indicates that God created the law of Eiruv Tavshilin when we know that this was a rabbinical enactment?
Why Shabbat and holidays are different in the Bible?
The wording of the biblical prohibitions against working on Shabbat and holidays are different and the rabbis interpreted the differences to mean that 39 categories of work are prohibited on Shabbat, including cooking and transferring a fire from one candle to another, but cooking and igniting a fire from an existing fire are allowed on holidays for foods consumed on the holiday. The rabbis also understood that, according to the Bible, if the day following the holiday is Shabbat, cooking is allowed on the holiday for Shabbat. However if the day following the holiday is not Shabbat, the rabbis understood that the Bible prohibited cooking on the holiday for a regular week day.
What did the rabbis do and why?
The rabbis instituted a non-biblical law that despite the Bible allowing cooking and transferring fire on the holiday if the next day is Shabbat, they prohibited it. They did so to avoid Jews making a mistake and thinking that since they are permitted to cook and transfer fire on the holiday for Shabbat, they are also allowed to do so on the holiday for a week-day. The rabbis were protecting Jews from a violation of a biblical prohibition of doing these acts on the holiday for a week day.
It is important to note that the prohibition for cooking and transferring a fire for Shabbat on the holiday is a rabbinical mandate – it is allowed according to the Bible – and the rabbis instituted the law to save the people from violating a biblical law not to cook on the holiday for a weekday. Once this is recognized, it will be clear that the rabbis could implement their own law as they see fit, and they did so to alert Jews not to cook on holidays for week-days.
What is the Eiruv Tavshilin Procedure?
Jews are told to take some bread or matzah before the holiday begins and a cooked food, such a hardboiled egg, a piece of fish, or chicken, which will be put aside and eaten on Shabbat. Jews hold the two items and recite a blessing thanking God “who mandated the commandment of Eiruv.” Jews should then recite a declaration that was originally composed in Aramaic, which states in essence that with this Eiruv it becomes permissible to bake and cook food and light Shabbat candles on the holiday for Shabbat. The Eiruv is then set aside to eat on Shabbat.
The Eiruv, in essence, is a ceremony whose sole purpose is to teach a lesson.
Why was the declaration composed in Aramaic?
Aramaic was the language spoken by most Jews at the time this procedure was instituted. The rabbis wanted Jews to understand what they were doing; that this procedure allowed them to perform acts for the sake of Shabbat only if the Eiruv was performed, but without an Eiruv or when a week-day followed the holiday, work was prohibited on the holiday for the next day. While the declaration is in Aramaic, Jews can read and recite it in any language they understand.
What happens when a Jew forgets to perform the Eiruv?
The rabbis covered this situation by instructing synagogue rabbis and community leaders to add to their declaration that they are performing the Eiruv for all who did not do so. Since the purpose of the Eiruv is to inform Jews not to cook foods or light candles on the holiday unless the holiday is followed by Shabbat and then only with an Eiruv, how do the rabbis and community leaders’ Eiruv accomplish the Eiruv’s goal? Rabbi and community leaders are encouraged to announce that they made the Eiruv for everyone who failed to do so.
Why does the Eiruv blessing say that God decreed the Eiruv law?
The rabbis understood the Torah to grant them authority to institute new laws. Therefore they created blessings for both biblical and rabbinical laws that indicate they were commanded by God, for God mandated Jews to obey rabbinical laws.
The Eiruv Tavshilin is designed to provide fresh cooked food for Shabbat and to allow Jews to light candles (actually transfer light from an already existing fire) on the holiday for Shabbat. The Torah does not prohibit doing such acts on holidays for Shabbat, but does not allow doing these acts on the holiday for a weekday. The rabbis instituted the law that forbids doing these acts on the holiday for Shabbat lest Jews think that since they can cook and light candles for Shabbat; they can do so also for the next day when it is a weekday. However, they made an exception to their own prohibition, the Eiruv. By instituting the Eiruv, they accomplished their purpose of reminding Jews that they may not do these acts on the holiday followed by a weekday.
The rabbis did not develop a procedure to get around a biblical law. They instituted their own law to protect Jews from violating a biblical law, and they build into their law a way that Jews would both remember not to cook and light candles on the holiday followed by a weekday and still be able to prepare foods and light candles for Shabbat.
 Such as September 2014 when the two day holiday of Rosh Hashanah on Thursday and Friday is followed by Shabbat on Saturday.
 While creating a new fire is not allowed on the holiday when Jews should have an enjoyable rest, taking a flame from an already existing fire is allowed on holidays. But on Shabbat, when stricter laws exist, transferring a fire is prohibited.
 The Torah gives no reason for the Shabbat prohibited acts. Many think that the prohibited acts are “creative acts.” Jews cease doing creative acts on the Sabbath to remind them that there is a God who created the world, ceased creation on the seventh day, and ordered Jews to also cease doing creative acts on the seventh day to remember God and the divine involvement in creating the world.
 The holiday is a day of rest from work, so work should not be done on a holiday for a week-day.