There is a lesser-known custom not to give a knife as a gift. This is because throughout Scripture metal (iron), especially a sharp object such as a knife, represents death and warfare. For this reason, it was forbidden to use iron tools in the construction of the Beit Hamikdash, as the Beit Hamikdash represents peace and life![1] One should not even bring a knife into a synagogue.[2]

It might just be that the source for not giving a knife as a gift is a superstition that originates in the writings of Rabbi Nachman of Breslov. It is written in the Sichot Haran,[3] in the name of the Baal Shem Tov, that “a knife should not be given as a gift, which means one should not give his friend a knife for a gift.” No further information is offered. It is likely based on the teaching that metal represents death and warfare. A gift is supposed to bring feelings of bonding and affection, and giving a symbol of warfare is not the ideal manner to convey these sentiments. It may also be a derivative of some ancient non-Jewish superstitions.[4]

It is also believed that giving a knife as a gift will negatively impact one's mazal, good fortune. There is a somewhat similar custom cited in the "Shemirat Hanefesh" not to lend one’s wallet or purse to others as doing so is said to transfer one's good fortune to the borrower.[5] The "Shemira Me’alya," a commentary printed alongside the Shemirat Hanefesh, notes that "for the same reason, I have a tradition that one should not give his friend a knife for a present." This is likely based on the idea that a knife is symbolic of one's livelihood, and perhaps giving someone a knife might negatively affect it.[6] The custom is also cited in "Shemirat Haguf V'hanefesh."[7]

One who chooses to give a knife as a gift is advised to also give some money along with it in order to neutralize any negative effects that giving a knife might have. There is an opinion that the aversion to giving a knife as a gift only applies to used knives. According to this approach, there is no problem with giving a new knife as a gift. Furthermore, the custom of not giving a knife as a gift is not cited in any of the primary halachic codes. Therefore, it is ultimately permissible to do so.[8] Even those who otherwise counsel against giving a knife as a gift generally permit doing so when the knife is being given in the context of a mitzva. For example, one may give a shochet a new shechita knife, a mohel an izmail, or a cutlery set to a bride and groom to help them set up their new home.

Many individuals have the custom to cover or remove any knives that are on the table before reciting the Birkat Hamazon.[9] This is because knives, reminiscent of swords, are items that shorten life, while the table, which represents the altar of God, lengthens it.[10] Another reason to cover or remove the knives is that there was once an individual who became so distressed at the mention of Jerusalem during Birkat Hamazon that he took a knife that was on the table and stabbed himself with it.[11] It also serves to recall the teaching that the Angel of Death has no power over those who recite Birkat Hamazon carefully and with concentration.[12] It is not necessary to cover or remove the knives on Shabbat and holidays as the holiness of these days protects us from any possible trouble.[13] Plastic knives need not be removed or covered.[14] It is noted that most people are not especially particular to observe this halacha and a number of contemporary authorities have justified their conduct.[15]

There is also a widespread custom not to use iron in the performance of mitzvot which is why many people avoid using iron mezuzah cases, and the like.[16] So too, many people avoid cutting their tzitzit strings with a knife or scissors. Teeth, a plastic knife, or ceramic scissors are often used for this purpose instead.[17]

We are taught that God delegates many tasks to angels. The angel in charge of providing people with sustenance and livelihood is the angel "Chatach," which literally means "to cut." Furthermore, we are required to concentrate intensely on the verse "pote'ach et yadecha u'masbia lechol chai ratzon” (“You open Your Hand and satisfy the needs of every living being”) when reciting "Ashrei," which refers to God as the provider of every person’s sustenance.[18] The final letters of the words "pote'ach et yadecha" spell out the name “Chatach.” Finally, the gematria of the word "u’masbia" is 428 which is the same gematria as the word "Chatach," yet another reference to the angel of sustenance.

There is a somewhat widespread custom to buy new knives each year before Rosh Hashana in order to arouse the power of Chatach. This is because Rosh Hashana is a time when one's livelihood and sustenance are being decided for the coming year.[19] In a variation of this custom some people have the custom to sharpen their knives.[20] It is also taught that the presence of a knife has the power to overpower and neutralize evil forces.[21] Some even have the custom to keep a knife in their pocket throughout Rosh Hashana for this reason! It is reported that Rav Yaakov Yitzchak of Lublin, “The Chozeh of Lublin,” would distribute knives as gifts to his chassidim on Rosh Hashanah as a segula that they become wealthy.

There is also a custom to sharpen one's knives every Friday in honor of Shabbat.[22] The reason for this is to ensure that there will be no knife-related problems or complications during the Shabbat meals. Indeed, one should always ensure that one's knives have no nicks, especially those that are used for eating on Shabbat.[23] Sharpening knives before Shabbat is also said to be a segula for shalom bayit.[24] So too, as mentioned, a knife is said to have the power to ward off evil forces, which is appropriate in advance of Shabbat.

[1] See Shemot 20:22; Devarim 27:5; Middot 3:4 with commentaries. See also Yalkut Shimoni, Kedoshim.

[2] OC 151:6; Kol Bo 17.

[3] Sichot Haran 9.

[4] See: http://en.wikipedia.org/wiki/Knife#Rituals_and_superstitions.

[5] Shemirat Hanefesh 153.

[6] Segulot Haba'al Shem Tov V'talmidav 81.

[7] Shemirat Haguf V'hanefesh 243:2.

[8] Chayei Halevi 2:87:5, 6.

[9] OC 180:5; Rokei'ach 332; Sefer Chassidim 102; Sefer Kushiot 84; Kitzur Shulchan Aruch 44:4; Kaf Hachaim, OC 180:15. For more on covering vs. removing the knives see: Shibolei Haleket 155; Kaf Hachaim, OC 180:15; Rivevot Ephraim 8:76:2.

[10] Shulchan Aruch Harav, OC 180:6; Mishna Berura 180:11; Shibolei Haleket 155. See also Rashi, Shemot 20:22. Even if the knives are made of gold or silver (metals from which swords are not generally manufactured) they should still be covered (Siach Yitzchak 95).

[11] Shibolei Haleket 155; Beit Yosef, OC 180; Kitzur Shulchan Aruch 44:4; Mishna Berura 180:11.

[12] Elya Rabba 180:6.

[13] Shulchan Aruch Harav, OC 180:6; Rivevot Ephraim 7:250:3. See also Magen Avraham 180:5. For an interesting discussion on whether the knives have to be covered when reciting Birkat Hamazon at night see: Rivevot Ephraim 1:136, 8:346. Regarding covering the knives at the Melave Malka meal see: Ohr Yitzchak 117.

[14] Rivevot Ephraim 7:250:3; Az Nidberu 7:2.

[15] Kitzur Shulchan Aruch 44:6; Aruch Hashulchan, OC 180:6. See also Or Yitzchak 56 for some interesting commentary on this custom.

[16] Daat Kedoshim, Hilchot Stam 289:1; Afarkasta D'anya 99.

[17] Mishna Berura 11:61; Shulchan Aruch Harav, OC 11:24. The Leket Hakemach Hachadash 11:23 notes that this custom is not found in the Talmud or any early sources. The Beit Baruch 11:161 writes that the preference for not using metal for cutting tzitzit strings only applies before they are first tied to the garment. Once they have been tied to the garment it appears that there would be no hesitation to use metal to cut them, though others are more stringent. See Kaf Hachaim, OC 11:12,17.

[18] Tehillim 145.

[19] Nitei Gavriel 11:10.

[20] Minhag Yisrael Torah, OC 482:20.

[21] Minhag Yisrael Torah, OC 482:20.

[22] Rema, OC 250:1; Likutei Maharich, Erev Shabbat; Kaf Hachaim (Palagi) 27:33.

[23] Minhag Yisrael Torah, OC 250:2.

[24] Mishna Berura 250:5.