Halakhah su Genesi 27:40

One also has to careful when about to say birkat ha-mazon to remove the knife from the table. The reason for this practice is because the table is called an “altar,” and just as on an altar we have been warned not to brandish something made of iron over it, as it is said, “do not build it [an altar] of hewn stones, etc.”¹⁹⁴Ex 20:22. The rule of Torah is that if one makes it into an altar of hewn stones with a tool of silver or flint, it is permitted. For the point of the prohibition is not against it being hewn, but rather because it is hewn with something made of iron, i.e., a sword, and Torah kept it far from the tabernacle, when it is written: “gold, silver, and copper,”¹⁹⁵Ex 25:3. but does not mention iron there. And likewise with the sanctuary it is written, “No hammers or axe or any iron tool was heard in the House when it was being built.”¹⁹⁶I Kings 6:7. The reason is because that is the power of Esau with what he was blessed from his father’s mouth; this is what is meant by “By the sword you shall live,”¹⁹⁷Gen 27:40. and it is written, “but Esau I hated.”¹⁹⁸Mal 1:3. Therefore it is kept far from the sanctuary. And likewise at the table we have been warned to remove the sword from it, because the sword is something destructive¹⁹⁹The pun ha-herev hu ha-mahriv is lost in the translation. and the source of destruction, the opposite of peace, and it does not belong in a place of blessing, i.e., peace. For indeed the altar and the table prolongs a person’s days, while a sword shortens them, and it makes no sense to brandish something that shortens over something that prolongs life.²⁰⁰Mekhilta Yitro (end).