By Rabbi Berach Steinfeld
In Devarim, Perek Chof Zayin, posuk heh it says that one is prohibited from lifting metal over a mizbeach. The Shulchan Aruch, in siman kuf peh says that the minhag is to cover the knife on the table while saying birkas hamazon. The Bais Yosef brings down two reasons for this minhag. The first reason is that a table is compared to a mizbeach and just like one may not raise a knife on a mizbeach, we cannot have a knife on the table while we bentch. Secondly, there was once a person who was bentching and when he mentioned that we do not have the Bais Hamikdosh he was overcome with depression and stabbed himself with the knife that was on the table near him. The chachamim therefore made a takana that knives should not be on the table during bentching.
If according to the first reason we say that the table is compared to a misbeach, doesn’t that apply to the whole meal? Why isn’t the knife forbidden to be on the table the entire time? The Pri Megadim in the Eishel Avraham explains that since we say in birkas hamazon “ve’al shulchan zeh sheachalnu alav” the takana of not having a knife on the table is appropriate for birkas hamazon.
Would one need to remove a plastic knife from the table during birkas hamazon? Would one need to remove a knife while saying al hamichya?
The Taz says that the takana of removing knives from the table was set up according to the way the story took place and since the story occurred with a metal knife during bentching, the gezeira applies to a metal knife during bentching. The Taz says that this is the reason why on Shabbos and Yom Tov one does not need to remove the knives from the table because the story mentioned above took place during the week. The only question is that this only satisfies the second reason of the Bais Yosef. We would still have the question of Shabbos and Yom Tov and al haminchya according to the reasoning that one’s table is considered a mizbeach. In addition, why is just the knife forbidden if yeast and honey were forbidden on the mizbeach as well? Shouldn’t they also be prohibited during bentching?
The answer is that the main reason was the second one mentioned, the first reason is just a remez; therefore during birkas hamazon when we use the words “al shulchan ze shachalnu alav” we are more liable to lose our emotions. The gezeira was not established on Shabbos and Yom Tov when we have some extra simcha.
May we all be zocheh to eat from the mizbeach to which our shulchan today is compared!