Shabbos, Chapter 6, Mishnah 2. In the previous mishnah we dealt with the items a woman may not wear out into a public domain, and now the mishnah turns to the man: which items may a man not wear when he goes out into a public domain on Shabbos.
"Lo yeitzei ha'ish b'sandal ham'sumar" - a man may not go out in a nailed sandal:
A sandal with nails fastened into it. The reason for the prohibition lies in a tragic incident that took place at a time when a decree was issued against the Jews forbidding them to keep Torah and mitzvos. They were hiding in a cave, and they thought they heard the sound of enemies breaking in. So that they would not be forced into apostasy and made to convert, Heaven forbid, they decided, as happened many times throughout Jewish history, that it was better for them to take their own lives, and they used the nails in their shoes for this purpose. In the end it turned out that there were no enemies there at all; it was a case of mistaken identification. Because of this the Sages decreed that one may not wear a nailed sandal, so that such a thing should not happen again.
The Gemara asks: why was the matter not forbidden on weekdays as well, and what does it have to do specifically with Shabbos? It answers: the incident itself occurred on Shabbos, and furthermore the prohibition belongs on Shabbos and Yom Tov because those are the times when people gather together. This is similar to certain prayers that are said specifically on Shabbos because the congregation is assembled together.
"V'lo b'yachid" - and not in a single shoe:
One may not go out wearing only one shoe, as opposed to wearing two shoes on both feet. There are two reasons for this:
People may suspect that he is carrying the second shoe with him.
People may mock him for wearing a single shoe, and as a result he will come to remove that one too and carry it in his hand.
This applies specifically when there is no wound on his foot. But if he has a sore on the foot that he is not covering, everyone understands why he is not wearing the second shoe: he is not suspected of carrying it, and he is also not mocked, since he has a logical reason for wearing only one shoe.
"V'lo bitefillin" - and not in tefillin:
A person may not go out while wearing tefillin, since Shabbos is not the time for the mitzvah of tefillin, and they therefore have the status of a burden. However, since they are worn and there is an aspect of normal wearing in them, the prohibition is only rabbinic. And even according to the opinion that holds that Shabbos is a time for tefillin, one still does not go out in them, out of concern that he may need to remove them and will come to carry them in a public domain.
"V'lo b'kamia bizman she'eino min hamumcheh" - and not with an amulet when it is not from an expert:
An amulet containing certain prayers or names of the Holy One, blessed is He, and sometimes certain herbs. One may not go out with it when it was not made by an expert. But if it was made by an expert, we are not concerned that he will remove it and come to carry it.
Instruments of war:
"V'lo b'shiryon" - and not in body armor, a tunic of chain mail rings.
"V'lo b'kasda" - and not in a kasda, a metal helmet.
"V'lo b'magafayim" - and not in magafayim, metal-plated boots.
All of these items are used only in time of war, and therefore the Sages said that one may not go out in them on Shabbos.
"V'im yatza - eino chayav chatas" - and if he went out, he is not liable to bring a sin offering: one who goes out with any of these items does not become liable to bring a chatas offering, since this is not a Torah prohibition but a rabbinic one.
In summary: in this mishnah we learned the items with which a man may not go out into a public domain on Shabbos: a nailed sandal, because of the incident that occurred in the cave; a single shoe, out of concern for suspicion or mockery, unless he has a wound on his foot; tefillin, since Shabbos is not their time and they are like a burden; an amulet that is not from an expert; and instruments of war - body armor, a helmet and metal boots. And in all of these, if he did go out, he is not liable to bring a chatas, since the prohibition is only from the words of the Sages.