Do we say at the Chuppah: Two Witnesses, excluding others?
At the chuppah, it is a time-honored custom to designate two Torah-observant men, unrelated to the wedding party or to each other, as eidei kiddushin (witnesses to the betrothal). This is to ensure that the kiddushin take place according to halachah, which demands the presence of two kosher witnesses to observe the chosson (groom) handing the ring to the kallah (bride). The designation takes place by announcing the names of the two kosher witnesses and asking them to come forward as eidei kiddushin. There is a newfangled addition some have introduced to this tradition: when the witnesses are called forward, an announcement is made: “These are the witnesses, to the exclusion of all others.”—or if Hebrew is more familiar, “Rak atem eidim” (Or the chosson—groom—may announce “rak atem eidai.”)
What are the benefits and pitfalls of this particular practice, a custom without halachic precedent? (After all, our ancestors had kosher weddings for generations without it!)
Those who have instituted this practice do so, as stated, to exclude the guests in attendance who are krovim u’pesulim (relatives or otherwise invalid witnesses)—since halachah says that “eidus shebatlah miktzasah batlah kulah” (testimony that is partially overthrown is completely nullified). A single invalid witness in a group of kosher eidim can invalidate the testimony altogether.
Now, there are many halachic authorities who rule that since the krovim u’pesulim have no intention of being eidim, they do not invalidate the kiddushin. Certainly, it would be deemed sufficient that the chosson and kallah are aware of who the (kosher) witnesses are.
There are others who maintain that the rule of nullified testimony applies exclusively to witnesses at the Beis Din; the rule does not extend to witnesses of kiddushin who aren't testifying in court, and the marriage is valid if any two kosher witnesses are present.
Nevertheless, the common practice is to actually appoint two kosher witnesses as a way of satisfying all opinions: “We call upon…and…to come forward as eidei kiddushin.” Designating witnesses automatically excludes all those who are not kosher. There are practical advantages to the designation of kosher witnesses: the guests standing closest to the chosson and kallah are often relatives, and otherwise kosher eidim may become preoccupied with other aspects of the affair and not observe the actual kiddushin—unless they are specifically asked.
When appointing two witnesses, other potentially kosher witnesses aren't necessarily excluded. Indeed, there were once communities where the tradition was to announce, “All kosher witnesses are designated as eidim.” Furthermore, there may be negative ramifications to “excluding all others.” In a case where we need to establish testimony of the kiddushin after the event and the designated eidim aren't available, or if one of the eidei kiddushin is later found to somehow be invalid as a witness, we can perhaps rely on other attendees as witnesses, and the kiddushin can thereby remain kosher.