"Eikev asher shema Avrohom bekoli” “Because Avrohom listened to My voice” Ch. 26, v. 5
The Gemara Yoma 28b derives from our verse that Avrohom even kept Rabbinical decrees, including Eruvei Tavshilin. Why is this particular law singled out?
1) The GR"A answers that in the original text of the Gemara the abbreviation E"T (ayin tes) appeared. A later transcriber mistakenly thought it stood for Eruvei Tavshilin, while it actually stood for Eruvei Techumin. This is rightfully alluded to in our verse by the word "Eikev" which also had the meaning "heel," hinting to the restriction of walking a certain distance beyond one's domain, which can be altered with Eruvei Techumin.
2) The Chasam Sofer answers that the words "eruvei tavshilin" mean mixture of cooked objects, meat and dairy cooked together. It is indeed unique that Avrohom kept this law since Tosfos on the Sanhedrin 4b d.h. "derech" say that there is a Torah restriction on Bosor b'cholov only when each on its own was originally permitted. Since before the Torah was given there was no verse to permit milk products, as they are an extract, "yotzei," from a prohibited object, namely a live animal, eiver min hachei (see Bechoros 6b), he really was permitted to eat this cooked mixture. Therefore, the Gemara Yoma stresses that he kept even this prohibition.
3) The Avnei Nezer quotes the Ramban who asks why there is a prohibition to prepare from Yom Tov to Shabbos, since Shabbos is greater than Yom Tov in all aspects. The Ramban answers that there is one point in which Yom Tov is greater. Yom Tov is established by a human court, while Shabbos is Divinely established. Human involvement to establish the right time for each Yom Tov is greater than a permanently set time, even if done so by Hashem. Therefore, it is prohibited to prepare on Yom Tov for Shabbos without making an eruv tavshilin. The Avnei Nezer says that since Avrohom (before the Torah was given) kept the Shabbos out of his own volition, his Shabbos was equal to Yom Tov even in the area pointed out by the Ramban. Therefore, there should be no restriction for Avrohom even without an eruv tavshilin, yet he still made one, maintaining the rabbinical decree.
4) Iyun Yaacov states that there is a halacha that one may not cook food on Yom Tov to be consumed even that same day by one who does not observe Shabbos and Yom Tov (see Shulchan Aruch O.Ch. #512:1). An eruv tavshilin would therefore not be applicable in Avrohom's situation, since Avrohom did not have the possibility of unexpected Shomer Shabbos and Yom Tov guests arriving, (which is a necessary component of the heiter created by the eruv, see #527 and Ran, Ch. 3 of Gemara Pesachim). Yet, he still made an eruv tavshilin to go through the motions of a future Rabbinical mitzvah.
The Baal Haturim points out that the word עקב which has a numeric value of 172, as the years that Avrohom listened to G-d’s voice. Avrohom lived 175 years. For the first 3 years he did not yet listen to G-d’s voice (recognized his Creator at the age of three per Nedarim 32a) but did for the next 172 years.
ERUVEI TAVSHILIN
(a) Although the Torah prohibits cooking and doing Melachah on Yom Tov for a weekday, when Yom Tov falls on Erev Shabbos, it is permitted mid'Oraisa to cook and to perform Melachos on Yom Tov for Shabbos (Pesachim 46b). The Rabanan, however, prohibited these Melachos unless an Eruv Tavshilin is made on Erev Yom Tov.
(b) (Beitzah 16b) Some hold the reason is to honor the Shabbos, by serving as a reminder that one should save food for the Shabbos meals. Others feel that it is meant to honor the Yom Tov, so that one should say, "It is prohibited to cook on Yom Tov even for Shabbos (without an Eruv Tavshilin), all the more so on Yom Tov for a weekday."
(c) An Eruv Tavshilin is made with a k'Zayis of cooked food (Beitzah ibid.) set aside on Erev Yom Tov to be eaten on Shabbos. When setting it aside, one says, "Through this Eruv we shall be able to bake, cook and do other necessary preparations on Yom Tov for Shabbos," after reciting the appropriate blessing.
ERUVEI TECHUMIN
(a) A person is only allowed to walk a distance of 2000 Amos, approximately 960 meters (3147 feet) or 1,152 meters (3774 feet), from his city or dwelling place (if he is not in a city) on Shabbos or Yom Tov. If he wants to walk another 2000 Amos, he must make an Eruv Techumin.
(b) This is accomplished by placing an amount of food that would be used for two meals nearly 2000 Amos away from his present location, in the direction in which he wishes to walk. The location where his food is placed is considered his new dwelling or place of Shevisah for that Shabbos or Yom Tov, and he may walk 2000 Amos in any direction from there.
(c) The food used for an Eruv Techumin may even be food that the person may not eat, such as wine for a Nazir and Terumah for a non-Kohen, since it can be eaten by someone else.
