The custom in our community is that at the Berit of a firstborn, the paternal grandfather is given the honor of serving as Sandak, and that his name is given to the baby.
The role of Sandak is to hold the infant at the time of the Berit Mila, and this is considered a very special Misva and a very special privilege. The Rabbis teach us that the one who holds the infant during a Berit is comparable to a Kohen offering Ketoret (incense) on the Mizbe’ah in the Bet Ha’mikdash. The Sandak resembles the Kohen; the infant resembles the Ketoret; and the Sandak’s lap resembles the altar. For this reason, the work Berit Abot writes that the Sandak should actively participate by taking the child from the father and placing him on his lap. As the Sandak resembles a Kohen performing the ritual of Ketoret, he must actually place the infant on his lap, rather than sitting passively and having somebody else put down the baby.
It is proper for a Sandak to immerse in a Mikveh before the Berit, just as a Kohen must ensure to be pure when performing the service in the Bet Ha’mikdash.
The comparison between a Sandak and a Kohen offering the Ketoret applies also to the blessing of wealth which is earned through the performance of the Misva. The Gemara teaches that offering the Ketoret had the power to bring the Kohen wealth, as indicated by the Pesukim in Sefer Debarim (33:10-11), in which Moshe speaks of the Kohanim offering Ketoret ("Yasimu Ketora Be’apecha") and then blesses them with wealth ("Barech Hashem Helo"). By the same token, performing the Misva of Sandak has the power to bring a person wealth. For this reason, it was customary in some communities (such as the community of Saloniki) not to serve as Sandak more than once a year, in order to allow other people to earn the great merit of this Misva and be worthy of this blessing of wealth. This is not, however, the custom in our community.
Technically speaking, it is permissible for a woman to serve the role of Sandak, though as a practical matter, this should not be done, as it would be immodest for a woman to sit among the men. In our community, it is customary for the child’s grandmother to bring the infant into the synagogue at the time of the Berit Mila. Some Rabbis disapproved of this practice, considering it inappropriate for a woman to enter the men’s section of the synagogue, but our community has accepted this custom. It goes without saying that the grandmother should be dressed appropriately.
If the Berit is held on a Monday or Thursday morning, and the father, Mohel and Sandak are all Yisraelim, such that there is only one Aliya available for the three of them, the Aliya is given to the Sandak, because his stature is considered the greatest of all three. This is mentioned by the Rama (Rav Moshe Isserles, Cracow, 1530-1572), in Yoreh De’a (266). One reason is because the father is merely fulfilling his obligation, and the Mohel is performing his job for which he is paid, whereas the Sandak fulfills this Misva voluntarily. Additionally, however, we might explain that since, as mentioned, the Sandak resembles a Kohen, he receives the Aliya just as a Kohen always receives precedence.
When it comes to the honor of serving as Hazan, however, this honor is granted to the Mohel. This is inferred from the verse in Tehillim (149:6), "Romemot Kel Bi’gronam Ve’hereb Pipiyot Be’yadam" – "The praises of the Almighty are in their throat, and a double-edged sword is in their hand." This verse alludes to the fact that the one holding the "sword" – meaning, the Mohel, who holds the knife for circumcision – should be the one to lead the proclamation of G-d’s praises, by serving as Hazan.
The Kabbalists teach that serving as Sandak has the unique ability to transform the "Mekatregim" – the angels that prosecute against us before the Heavenly Tribunal – into "Sanegorim" – advocates arguing on our behalf. The word "Sandak" has been read as an acrostic for the phrase "Sanegor Na’asa Din Kategor" – the harsh judgments of the prosecutor become an advocate. Normally, we try through different methods to silence the prosecuting angels. But through the Misva of serving as Sandak, we can do even better – and actually have these angels advocate on our behalf. To appreciate what this means, let us imagine a prosecutor standing up in a courtroom and speaking in praise of the defendant, explaining to the court why he deserves to be acquitted. This is what we accomplish through the great merit of serving as Sandak.
The Arizal (Rav Yishak Luria, 1534-1572) taught that the Misva of serving as Sandak has the effect of rectifying sins involving the Berit Mila. This can be explained through the concept of "Teshubat Ha’mishkal" – that we atone for sins by performing Misvot associated with the sin that was committed. For example, our Sages teach that we can atone for the grave sin of Lashon Ha’ra (negative speech about other people) by using our mouths to speak words of Torah. This is inferred from the 12th chapter of Tehillim, which speaks of the severe punishment for forbidden speech ("Yachreit Hashem Kol Sifteh Halakot" – 12:4), and then speaks of the unique purity of words of Torah ("Imrot Hashem Amarot Tehorot" – 12:7). Likewise, by taking an infant and placing him on his lap to be circumcised, the Sandak atones for sins which he committed involving the Berit Mila.
In some communities, it is customary to approach the Sandak after a Berit to ask him for blessings. Apparently, it is felt that given the special merit of this Misva, the Sandak at that time is endowed with the special ability to confer blessings.
There is a tradition that when the infant cries during the Berit, this is an especially auspicious time to pray for whatever one needs. However, many people make the mistake of forgetting that the most important prayer to recite at this time is a prayer for the welfare of the child. It would be exceedingly selfish at that moment, when hearing the baby cry in pain, to pray only for oneself, ignoring the child’s suffering. We would never imagine hearing a patient crying in pain from his hospital bed and responding by reciting a prayer for our own wellbeing. By the same token, when the infant cries at a Berit, one should first pray for the child, and then pray for whatever needs he has. Indeed, Rav Eliyahu Gutmacher (1795-1874), in his notes to Masechet Shabbat, writes explicitly that the primary prayer to be recited at the time the infant cries is for the infant himself. (Incidentally, the blessing of "Refa’enu" is the eighth blessing of the Amida prayer because it is a prayer for infants who are circumcised on the eighth day and need G-d’s help to be healed. This is why the blessing ends by describing G-d as "Rofeh Holeh Amo Yisrael" – the Healer of the Jewish People, as opposed to the "Asher Yasar" blessing, which concludes by describing G-d as "Rofeh Kol Basar" – Healer of all flesh. The Beracha of "Refa’enu" speaks specifically of G-d’s healing the Jewish People, and of His healing all people, because it refers to the newly-circumcised Jewish infants in need of healing.)
This point is relevant also to wedding ceremonies. There is a tradition that the Hupa ceremony is an auspicious time to pray, and many have the custom to distribute cards with the names of people in need of assistance for whom the guests are encouraged to pray during the ceremony. However, the guests must remember that the most important prayer to recite at that time is a prayer for the newlywed couple, that the marriage should succeed and they should be blessed with happiness, health and prosperity.
Summary: Serving as Sandak at a Berit (meaning, holding the baby during the circumcision) is a unique privilege, which renders one worthy of many great rewards. In fact, in some communities, it is customary not to serve as Sandak more than once a year, in order to allow more people to earn the great benefits of this special Misva. This is not, however, the custom in our community. According to some sources, the Sandak should actually take the infant with his hands and then place him on his lap, rather than remaining passive as the infant is placed on his lap. It is proper for the Sandak to immerse in a Mikveh before the Berit, as he is considered like a Kohen serving in the Bet Ha’mikdash. If, on the day of the Berit, the father, Mohel and Sandak all pray at the same Minyan, the Mohel is given the privilege of serving as Hazan. If this happens on a Monday or Thursday, when the Torah is read, and they are all Yisraelim, such that only one of them can receive an Aliya, the Aliya should be given to the Sandak.