As Avraham nears the end of his life, he must find a suitable wife for his beloved son Yitzchak. Since Avraham might not live to see this happen, he elicits a commitment from his chief servant, whom the Midrash (Bereshit Rabba 59:5) identifies as Eliezer:
And Avraham said to his servant, the senior member of his household, who administered all that was his: “Place, now, your hand under my thigh. And I make you swear (V’ASHBI’ACHA) by Hashem, G-d of the heavens and G-d of the earth, that you will not take a wife for my son from the daughters of the Canaanites, in whose midst I dwell” (Bereshit 24:2-3).

Then, Avraham clarifies the additional terms of the pledge: to try to select a wife from his relatives in Charan, but under no circumstances to take Yitzchak out of Canaan. And the servant placed his hand under his master Avraham’s thigh, and he swore to him about this matter (verse 9).

The Tanach cites a number of ways for one to demonstrate a commitment, including removing a shoe (Rut 4:7), and a handshake (Yechezkel 17:18; Mishlei 17:18, 22:26). Rashbam (R. Shmuel ben Meir, c. 1080-1174) and Haamek Davar (R. Naftali Tzvi Yehudah Berlin, “Netziv,” 1817- 1893) say that such actions occur between equals. “Placing the hand under the thigh,” on the other hand, is reserved for relationships of inequality, like master and servant. This accounts for the only other recorded instance of this action, but this time between a father and son:

And the days approached for Yisrael to die, and he called for his son, for Yosef, and he said to him: “If now I have found favor in your eyes, please place your hand under my thigh. And you shall render me kindness and truth: please do not bury me in Egypt.” … And he said, “Swear to me!” And he swore to him (Bereshit 47:29, 31). (It is reasonable to assume that Yosef obeyed his father.) Netziv points out that, as his master, Avraham is able to compel Eliezer to swear (V’ASHBI’ACHA); but Yosef is a free man, so Yaakov only requests him to swear. What is the meaning of “placing the hand under the thigh”? What connection is there between this action and swearing?

Some commentaries separate this act from the swearing that follows. It is purely an acknowledgement of subservience, as if to say, “behold my hand is in your domain to do as you will.” Ibn Ezra says this practice continues in India. Hirsch (Rabbi Shimshon Raphael Hirsch, 1808-1888) interprets the gesture contrarily:
“A dying man, or one whose end is approaching, … exacts a promise from one who will outlive him, to carry something out, without which he feels he cannot die in peace. … ‘Let me rest on your hand.’”

Rashi however, following the Midrash (Bereshit Rabba 59:8), connects “placing the hand under the thigh” to swearing. The Talmud (Shavuot 38b)rules that one must hold an object (nekitat chefetz) of inherent mitzvah- anctity, such as a Torah scroll, when swearing (this is certainly true of a Torah-mandated oath, and might also be advisable for Rabbinic oaths, although nowadays swearing is avoided). Nekitat chefetz is part of a process of imbuing the one swearing with a profound fear of swearing falsely or in vain. (See Rambam, “Laws of Swearing” 11:8, 11; Shulchan
‘Aruch Choshen Mishpat 87:13, 15, 17.)

In fact, the Talmud quotes our verse as the source for nekitat chefetz. However, as Tosafot point out, Avraham had not yet been commanded to fulfill any mitzvah other than circumcision. Rashi says thigh is a euphemism for circumcision: “… circumcision was the first mitzvah for him, and it came to him through pain, and it was beloved to him.”

Aruch HaShulchan (R. Yechiel Michel Epstein, 1829-1908) explains that nekitat chefetz requires the most beloved mitzvah-object available: for Avraham that was his own circumcision, whereas after Sinai it is a Torah
scroll. This is the precursor to the familiar practice of “swearing on the Bible.”

According to Rashi’s view, Yaakov merely followed his grandfather’s precedent. [Perhaps there is a further similarity between them: Like Avraham, Yaakov had a painful experience involving his thigh, when the angel he wrestled dislocated it (Bereshit 32:26). Midrash Lekach Tov says the angel, the “guardian of Esav,” wanted to challenge the merit of circumcision. This incident is the basis for another mitzvah, the prohibition against eating the gid hanasheh.]

Nekitat chefetz is so essential that without it the oath is invalid. It is remarkable to think, therefore, of Avraham’s act, although pre-Sinai, as the source of a law!

Is nekitat chefetz required by the Torah (d’Oraita), or is it a Rabbinic requirement which uses our verse, not as a source, but as support (asmachta)?

Tosafot and Rema (R. Moshe Isserles, c. 1525-1572, Choshen Mishpat 87:13) seem to be of the opinion that nekitat chefetz is d’Oraita: Torah law confirms what Avraham did. Rosh (Rabbenu Asher ben Yechiel, c. 1250- 327) and Rambam hold that nekitat chefetz is a Rabbinic requirement.

R. Moshe Feinstein (1895-1986) in Iggrot Moshe (Orach Chayim I 32:5) explains a practical difference between these positions, in the case of one who swore without nekitat chefetz, but when asked to repeat his oath with nekitat chefetz, he refuses. If nekitat chefetz is d’Oraita, then he has not sworn at all, and the court can confiscate his property. If nekitat chefetz is only Rabbinic, however, then his first oath is Biblically valid, and the court does not have the ability to confiscate his property (Shavuot 41a).

As he has done throughout his life, Avraham, in preparing for the continuity of the Jewish people, is a role model for Torah values. He shows that a commitment made in the presence of Hashem binds one, in the most intimate way, to Hashem and to His mitzvot.