1. One who finds teffilin [outdoors on Shabbat] should bring them in [wearing them] a pair at a time.
2. Rabban Gamaliel says, two [pair] at a time.
Our Sages considered it proscribed labor to carry any burden of value from one domain to another on Shabbat. As we noted last time, it is not the weight of an item that constitutes its significance in the Rabbinic mind, but the value that people ascribe to it. Some items have value because of their utility (food, for example), while others have value due to their sacred nature. One such sacred item is a pair of tefillin. In this mishnah, we see that one is prohibited from carrying tefillin from one domain to another (here, from the outdoors to indoors) on Shabbat, even to protect them from harm. Rather, the mishnah suggests, put on the tefillin and walk indoors. In this way, one preserves the sacred object without violating Shabbat.
But wait, some of you are probably thinking: we do not wear teffilin on Shabbat!
That is true, but according to the Talmud, the dispute in this mishnah has to with the reason why we do not wear teffilin on Shabbat. Position number one, that we should bring the lost tefillin in wearing them a pair at a time, takes the stance that Shabbat is, in fact, on a Torah level, an appropriate mitzvah-time to wear tefillin. But our Sages were concerned that if the strap of one of the tefillin broke while the person wearing them was out of doors, it would be carried home, and the Shabbat would be violated. Thus, according to this view, it was our Sages who prohibited the wearing of tefillin on Shabbat. Since they made the prohibition, they can also rescind it to save our lost pairs of tefillin. However, since it is only a mitzvah to wear one pair of tefillin at a time, one may not save more than one pair at a time by wearing them.
On the other hand, Rabban Gamaliel sees the exemption from tefillin as deriving from the Torah itself. The Torah calls tefillin a "sign" between God and Israel (in Deuteronomy 6:8, for instance). Shabbat is also called a "sign" (in Exodus 31:17, for example). In this view, the Shabbat "sign" subsumes and obviates the need for the tefillin "sign" on the sacred day of rest. There is no mitzvah of tefillin on Shabbat, but the tefillin are considered an adornment, like a fine piece of jewlery. And, as with jewels, one may wear more than one on Shabbat (at least to save them from destruction).