The Gemara teaches that Avraham Avinu observed the entire Torah despite the fact that it was given to Benei Yisrael only centuries later. Interestingly, the Gemara emphasizes that Avraham observed even the law of Eruv Tavshilin – setting aside food before Yom Tov to allow preparations on Yom Tov for Shabbat. The Halacha of Eruv Tavshilin was enacted by the Sages, and is not required according to Torah law. The Gemara thus emphasizes that Avraham observed not only Biblical commands, but Rabbinic enactments, as well.
Why would the Gemara specify the particular law of Eruv Tavshilin?
The Gaon of Vilna (Rabbi Eliyahu of Vilna, 1720-1797) suggested that the Gemara did not, in truth, mention Eruv Tavshilin in this context. It is possible, the Gaon claimed, that in the original texts of the Talmud this passage was written with the Rashei Teivot (acronym) "Ayin" - "Tav," which represented the words "Eruv Techumin." The term "Eruv Techumin" refers to the laws governing the distance one is allowed to walk outside his city on Shabbat. Copiers may have erroneously interpreted the acronym as referring to Eruv Tavshilin, rather than Eruv Techumin, and this erroneous reading became the standard text in published editions of the Talmud. The Gaon explained that the Sages inferred Avraham's observance of Eruv Techumin from the verse (Bereishit 26:5), "Eikev Asher Shama Avraham Be'koli" – "Since Avraham heeded My voice." The word "Eikev" ("since") can also mean "heel," and this verse thus perhaps alludes to Avraham's strict observance of a Mitzva relevant to walking, namely, Eruv Techumin.
The Da'at Zekeinim Mi'Ba'alei Ha'Tosafot (a compilation of Torah commentaries by the Tosafists) suggests a different approach, claiming that the Gemara uses the term "Eruv Tavshilin," which literally means "mixture of foods," in reference to the prohibition of milk and meat. The Gemara emphasizes that Avraham observed all laws in the Torah, including the prohibition against partaking of milk and meat.
If so, the question arises as to how Avraham allowed himself to serve both milk and meat to his visitors, as the Torah explicitly tells in the Book of Bereishit (18:8). If, indeed, he observed even the prohibition of milk and meat, why would he serve milk and meat together to his guests?
Some have explained that the prohibition of placing milk and meat together on the same table stems from the concern that one might eat them together. Therefore, if there is another person present watching to ensure that the individual does not mix the milk and meat, the prohibition against serving them together at the table does not apply. Now since, as the Torah tells in the aforementioned verse, Avraham stood over the visitors as they ate, there was no concern that they would eat the two kinds of foods together, and he was therefore allowed to serve meat and milk together at the same table.
Finally, the question arises as to why Avraham did not observe the Mitzva of Berit Mila (circumcision) until God commanded him to do so (Bereishit 17). If he observed all the Mitzvot, he should have circumcised himself and his son even before receiving an explicit divine command.
One answer, perhaps, is that without a divine command to perform circumcision, it would be forbidden on the grounds of Chabala – inflicting a wound in oneself. The Torah forbids causing oneself bodily harm and injury, and thus Avraham was not entitled to voluntarily perform circumcision. Only after God commanded him with regard to this Mitzva was the prohibition of Chabala overridden by the Mitzva.
A simpler answer, however, is that Avraham preferred to wait because of the principle that a "Metzuveh Ve'oseh" – one who performs a Mitzva regarding which he bears an obligation – receives more reward than a "She'eino Metzuveh Ve'oseh – one who performs a Mitzva regarding which he is under no obligation. When it came to all other Mitzvot, Avraham could perform them on a voluntarily basis and then, when the command is issued, observe them in fulfillment of his obligation. The Mitzva of Berit Mila, contrast, can be performed only once. Avraham therefore preferred to wait until he received the divine command, so that he would receive the great reward of a "Metzuveh Ve'oseh," rather than the lesser reward of a "She'eino Metzuveh Ve'oseh."
This discussion of Avraham's strict observance of Halacha even before Matan Torah should serve as a reminder to us of the immense importance of observing Halacha, in all its details. If the patriarchs ensured to comply with the dictates of Halacha even before they became obligatory, then certainly we, who were given the Torah, bear the responsibility to carefully fulfill each and every detail of Halacha.
