Question: May a soldier or a citizen armed with a pistol or a rifle enter a synagogue with his weapon?
Answer: The Mechilta (end of Parashat Yitro) states regarding the verse, “And when you shall build Me a stone altar, you shall not build it of hewn stone; for you will have waved your sword over it and desecrated it”: “Rabbi Shimon ben Elazar said: The Altar was created to prolong the life of man. Thus, one may not wave the ‘item that shortens’ (the item that shortens man’s life, i.e. a knife) over the ‘item that lengthens’ (the item that prolongs man’s life, i.e. the Altar).”
Similarly, regarding our question, the Orchot Chaim (Hilchot Bet Ha’Kenesset, Section 7) writes in the name of Maharam of Rottenberg that one may not enter a synagogue with a long knife, for prayer prolongs one’s life and a knife shortens it. Although Rabbeinu Peretz disagrees with the Maharam, Maran Ha’Shulchan Aruch (Chapter 151) rules in accordance with the opinion of the Maharam of Rottenberg. It is thus forbidden to enter a synagogue with a sword or a long knife. Although this law is not so common nowadays since people do not carry around swords, we must nevertheless discuss weapons such as rifles which are likewise made out of metal and shorten lives. It would seem based on the above that it should be forbidden to enter a synagogue with one’s personal weapon.
Maran Rabbeinu Ovadia Yosef zt”l (in his Responsa Yechave Da’at Volume 5, Chapter 18) explains that the Maharam does not prohibit entering a synagogue with a long knife only because a knife shortens one’s life; rather, he has an additional reason for this which is due to the respect of the synagogue, for it is disrespectful to enter a synagogue when one is armed with a weapon. He proceeds to support his view.
In the previous Halacha we have explained that it is customary to cover the knives on the table during Birkat Hamazon, for a knife shortens man’s life while Birkat Hamazon lengthens it. Based on this, the Turei Zahav asks: Why is it that it is only prohibited to enter a synagogue with a “long” knife? We do not find such a distinction between a long or short knife regarding Birkat Hamazon! He explains that regarding Birkat Hamazon where it is quite easy to cover all of the knives on the table, there is no reason for one not to do so. Nevertheless, regarding entering a synagogue where one will have to remove the knife completely a find a place to leave it in addition to the fact that there is sometimes a need to use a knife in a synagogue as well in which case one will have to go get it, our Sages did not trouble an individual to such an extent. However, with regards to a long knife which is not usually necessary in a synagogue, our Sages troubled one not to enter the synagogue with it at all.
Based on this, Maran zt”l writes that when there is a pressing need for one to carry his weapon and removing it proves to be a great hassle, it is not forbidden to enter a synagogue with it, similar to the law of a small knife. He proceeds to quotes sources and proofs to the fact that as long as there is a great need for one to carry the weapon, there is no prohibition to enter the synagogue and pray while armed with it.
Summary: It is preferable that an armed soldier entering a synagogue to pray cover his weapon with his clothing. If this is not possible, for instance, because one is armed with a large rifle, and there is a great need for one to be carrying his weapon, such as due to security concerns and the like, one may be lenient and enter the synagogue to pray in this manner.