Megillah, Chapter Four, Mishnah Eight
The next two mishnayot deal with certain practices which the rabbis deemed to be heretical or at least potentially heretical.
1) If one says, I will not pass before the ark in colored clothes, even in white clothes he may not pass before it.
2) [If one says], I will not pass before it in shoes, even barefoot he may not pass before it.
3) One who makes his tefillin [for the head] round, it is dangerous and has no religious value.
4) If he put them on his forehead or on the palm of his hand, behold this is the way of heresy.
5) If he overlaid them with gold or put [the one for the hand] on his sleeve, behold this is the manner of the outsiders.
Sections one or two: In the first two sections we learn of people who refuse to pass before the ark (to lead the Amidah) either while wearing colored robes or while wearing shoes. The rabbis suspected that one who demanded to wear white clothes or go barefoot may have had heretical beliefs. Therefore, they said that such a person cannot pass before the ark at all, even in white clothes or barefoot. In other words, wearing white clothes and going barefoot seem to have been valid practices but one who insists upon them is suspected of heresy.
We should note that the groups being described here seem to be taking Temple practice and applying it to the synagogue. In the Temple the priests robes were white and they went barefoot. The mishnah may be trying to emphasize that the synagogue is not the Temple and one who insists on dressing in the synagogue as if it were the Temple is potentially a heretic. There also may be a covert battle for leadership in this mishnah between priests and rabbis. Rabbis may be telling priests that when in the synagogue leading the Amidah (as opposed to reciting the priestly blessing) they are functioning as regular Jews and not as priests.
Section three: The boxes of tefillin are supposed to be square. Our mishnah deals with a period of oppression when the Romans prohibited Jews from wearing tefillin. In response someone makes his tefillin round so that the Romans will not notice that he is wearing tefillin. According to the mishnah this attempt is doubly mistaken. The Romans will realize that he is wearing tefillin and therefore it is still dangerous. Secondly, by making his tefillin round he is not fulfilling the mitzvah of tefillin. There is also the idea that tefillin can protect a person from danger. But since these tefillin are not valid they offer no protection from the Roman oppressors.
Section four: The Torah says that you should place tefillin as a sign upon your hand and as a remembrance between your eyes. Non-rabbinic groups of Jews (sectarians) interpreted these verses literally; tefillin are put on ones hands and on the forehead between ones eyes. The rabbis did not interpret the verses literallytefillin go on top of ones head, where the hairline ends, and on ones arms, next to ones heart. A person who wears his tefillin between the eyes or on the hand is acting as a heretic. I should note that I have seen many, many instances of people wearing their tefillin to low on their heads. One who wears tefillin between his eyes has not fulfilled his obligation.
Section five: Covering tefillin in gold or wearing them on ones sleeves is not proper fulfillment of the mitzvah. The mishnah deems this as the practice of outsidersthose who have separated from the rabbinic fold.