There is a minhag not to have the same  person be honored as a Sandek twice in one family. The Rama quotes the Maharil who likens a sandek to a Kohen who brings the ketores in the mikdash. The ketores was considered an important mitzvah and was a segulah for wealth. In order to create a fair society amongst the Kohanim,  they created a system so that no kohen should be able to bring the ketores more than once. During the daily gorel they would announce that only those Kohanim who have not bought the ketores should participate in the gorel.

Similarly, being Sandek at a Bris is a segulah for wealth and like the Kohen offering Ketores, it is limited to once per family.

But why is bringing a baby to the Bris likened to offering Ketores? What is the deeper connection between the Bris Mila and Ketores which causes us to equate them?

To understand the power of Ketores, let’s first take a look at the Parsha. After Korach and his cohorts are punished for their rebellion, Bnei Yisroel complained that Moshe and Aharon were responsible for killing the nation of Hashem. As a result, Hashem sends a plague to punish the Jewish people.

Moshe tells Aharon to offer Ketores to atone for the Jewish people. Why did Moshe suddenly pull out the Ketores? What is the connection to the impending plague? The Gemara explains that when Moshe was on Har Sinai to receive the Torah, each of the Malachim presented Moshe with a gift. Even the Malach Hamaves gave Moshe a gift, teaching Moshe the secret that Ketores has the ability to stop a plague. When Aharon burnt the Ketores amongst the Jewish people, the Malach Hamaves halted in his tracks, bringing the plague to its end.

What is the unique power of Ketores that it can stop a plague, even when the Jewish people seemingly deserved to be punished?

The Baal HaTanya explains that Ketores represents a very deep relationship between Hashem and the Jewish people. Unlike a Korban which comes from the word Karev suggesting an external closeness with Hashem, the word Ketores is related to the Aramaic Ketar – meaning a knot, suggesting a state of absolute oneness.

Ketores represents the innermost connection which a Jew has with Hashem. This connection exists at the very core of our Neshama, which is a part of Hashem. This connection is deeper than the connection to Hashem which is forged through keeping Torah and Mitzvos. It is like the love of a parent to a child which cannot be tainted by the child’s behavior, no matter what they do.

This was the secret of the Malach Hamaves! Ketores arouses this deep love and causes Hashem to shower this deep love on the Jewish people, no matter what they have done.

This is why the central Avodah in the Beis Hamikdash on Yom Kippur was the offering of Ketores in the  Kodesh Hakodoshim. As the day of atonement, our short-fallings in keeping the Mitzvos are erased when this deepest connection to Hashem is revealed.

Back to the Bris. The Baal HaTanya explains that the Bris Mila is even greater than Torah. Through Torah we relate to Hashem on the level of intellect – the Torah coming from the attribute of Chochma. A Bris represents a relationship with Hashem which is deeper and higher than intellect.

This is like two friends who make a pact (Bris) to retain their love for one another. Even when logic and circumstance may be reason for their love to dissipate, the Bris between them binds them together beyond logic and reason.

The Bris Mila, like the Ketores, represents our essential bond with Hashem. Like the power of Ketores, the merit of the Bris Mila saves a person from Gehennom.