By Rabbi Berach Steinfeld
The posuk says that upon arriving at the home of Rivkah, Eliezer said, “I can’t eat until I speak first.” The question arises; why could he not eat until he spoke? The Kedushas Levi clarifies based on the Rema in Even Ho’Ezer, siman samech alef and siman samech heh. There is a minhag that a chosson and kallah fast on the day of their wedding. Eliezer, who was the Yitzchok’s shaliach to be mekadesh Rivkah, could not eat until he finished the kiddushin.
This answer of the Kedushas Levi is dependent on a machlokes ha’poskim. In the Shulchan Aruch mentioned above, the commentaries explain two reasons why a chosson and kallah fast. The first reason is that the day of the wedding is considered like Yom Kippur since the sins of the chosson are forgiven as we see in the Yerushalmi in Bikurim, Perek Gimmel, halacha gimmel. The posuk, “Vayikach es Machlas” shows that when he married Machlas all his sins were forgiven. That is the reason the chosson and kallah fast on their wedding day. Others say that the reason for the fast is because the kiddushin has to be done in a sober state and if the chosson and kallah will eat, they may come to drink wine and thereby make their kiddushin ineligible. The difference between these two reasons would be whether a shaliach would need to fast. If the reason is that it is like Yom Kippur, it would be for the chosson and kallah themselves, not theshaliach. If the reason is that we need the kiddushin done in a sober state, which would apply to the shaliach also.
The Betzel HaChochma in Chelek Heh, siman kuf nun gimmel explains that in this case Eliezer needed to fast. He says that the reason why we don’t pasken that a shaliach needs to fast is because no shaliach would want to be a shaliach for kiddushin if it requires him to fast. This applies to a regularshaliach. However, in the case of Eliezer who had no choice and had to be the messenger, he was required to fast until he consummated the kiddushin.