The meal eaten to celebrate a Berit Mila has the status of a Se’udat Misva – a meal which fulfills a Misva. This meal is regarded with such importance that the Gemara in Masechet Pesahim teaches that one who is invited to such a meal and does not attend deserves Niddui (excommunication) for belittling this precious Misva. Moreover, the Kabbalists teach that the Satan expends great efforts to try to sabotage the Berit Mila meal, because of its great value. In fact, the letters that spell the Satan’s name – "Sin," "Mem," "Alef," "Lamed" – have been read as an acrostic for the words, "Se’udat Mila En La’asot" – "the Mila meal should not be performed," because the Satan sets out to disrupt the fulfillment of this great Misva.
The reason why this meal is so precious is because it demonstrates our immense love for even a Misva which entails great Mesirut Nefesh (self-sacrifice). The Misva of Berit Mila entails inflicting a wound on a newborn child, which is very distressing, and yet we not only perform the Misva, but celebrate it, showing our great love for Misvot. And for this reason, because this celebration is so valuable and precious, the Satan does everything it can to interfere.
Additionally, as Eliyahu Ha’nabi attends a Berit Mila, we must conduct a special meal in his honor, just as a special feast is customarily held to mark the arrival of a distinguished guest.
The earliest source of this Misva is the festive meal which Abraham Abinu hosted "Be’yom Higamel Et Yishak" (Bereshit 21:8), which our Sages understood as referring to the day of Yishak’s Berit Mila. The word "Higamel," which begins with the letters "Heh" and "Gimal," can be read as a reference to the Berit Mila ("Mal") on the eighth day (the combined Gematria of the letters "Heh" and "Gimal").
This meal is also alluded to in the verse in Tehillim (50:5), "Isfu Li Hasidai Koreteh Beriti Aleh Zebah" ("Gather for Me my righteous ones, those who enter My covenant, for a feast"). The Gemara states that one must attend a Berit Mila feast only if the other participants are righteous, upright people, and thus the phrase "Isfu Li Hasidai Koreteh Beriti" alludes to the righteous ones ("Hasidai") who have gathered to celebrate "Beriti" – a Berit Mila. The Mateh Moshe comments that the word "Zebah" in this verse, which is spelled "Zayin," Bet," "Het," may be read as "Zab Het" – "it flows on the eighth," alluding to the flow of blood that results from the circumcision performed on the eighth day.
The Rama (Rav Moshe Isserles of Cracow, 1530-1572) notes the practice widely observed among Ashkenazim to hold a special celebration in the infant’s home on the Friday night before the Berit, commonly called a "Shalom Zachar." The source of this custom is the Gemara in Masechet Baba Kama (80) which tells of a special meal called "Yeshu’a Ha’ben" (literally, "the salvation of the son"). Whereas Tosafot explain this as a reference to the meal held at the time of a Pidyon Ha’ben, when a firstborn boy is redeemed, Rashi explains that it refers to a celebration held before a child’s Berit Mila. This meal is called "Yeshu’a Ha’ben" because the child was "rescued" from the birthing canal. The process of childbirth is dangerous for an infant, and so after his birth it is appropriate to hold a special celebration. The Taz (Rav David Segal, 1586-1667) writes (Orah Haim 265) that this celebration is held on Friday night simply because this is the time when people are home and free to attend such an event in honor of the newborn child.
Another explanation for why this celebration is held specifically on Shabbat stems from a passage in the Midrash explaining why the Torah commands circumcising a child specifically on his eighth day. The Midrash draws an analogy to a king who wants to hold a feast, but he decides to delay the feast until the queen arrives. Similarly, the Midrash says, a child should not celebrate his Berit Mila, formally entering into the covenant with G-d, until the Shabbat queen arrives. It is only after the child has experienced a Shabbat that he can undergo Berit Mila, and the so the Torah commanded performing Berit Mila on the eighth day, ensuring that the child has experienced a Shabbat. It is thus appropriate to hold a special celebration for the child on his first Friday night, as the experience of Shabbat is what makes him eligible, in a sense, for Berit Mila.
There is also another explanation for this practice. The Gemara teaches that throughout the period when a child is in his mother’s womb, he studies Torah, and he in fact learns the entire Torah during this time. Just before he exits the womb, however, the angel that was with him strikes him on his lip – forming the cleft under the nose – which has the effect of erasing all the Torah knowledge from the infant’s mind. The Rabbis teach that during an infant’s first seven days of life, he observes a period of mourning for the great loss which he just suffered. In an instant, he went from having thorough knowledge of the entire Torah, more than that of the greatest Torah sages, to being completely ignorant, knowing absolutely nothing. This is why the Berit Mila is held on the eighth day, as it must be delayed until after the infant’s seven days of mourning, when he bemoans the loss of his Torah knowledge. On Shabbat, we come to the infant’s home to comfort him, like we visit actual mourners to offer comfort. This is done on Shabbat because Shabbat was given to us for the purpose of learning Torah. Our Sages teach that Shabbat and Yom Tob, when we are free from our work responsibilities, are the times allocated for involvement in Torah study. And so on the infant’s first Shabbat, we visit him in his home and comfort him by noting that he will, please G-d, have many Shabbatot throughout his life when he will have the opportunity to learn Torah and regain the knowledge which he lost.
The Satan tries everything it can to dissuade a person from incurring the expense and going through the trouble of conducting the Friday night celebration after an infant’s birth, and the Berit Mila feast. We must remember that these Misvot are exceedingly valuable and precious, and it is worth expending time, money and effort for this purpose.
