When a woman is widowed, she continues to be supported by the heirs to her late husband’s estate, in exchange for her work. Rabbi Yosei bar Hanina teaches that she is obligated to do all the work that she performed while her husband was alive, except for personal things like washing his face, hands and feet.
In the context of this discussion, the Gemara raises the issue of similar types of service that a student does for his teacher.
Rabbi Yehoshua ben Levi taught: A student should perform any service for his teacher that a slave does for his master with the exception of removing his shoes for him. Rava explains that this is only true in a place where the student is not known, and may be thought to be a slave; otherwise it would be appropriate to remove his teacher’s shoes. Rav Ashi rules that even in a place where the student is not known, if he wears tefillin he can perform such service, since the tefillin clearly indicate that he is not a slave.
Sources in both the written Torah and the Talmud make it clear that shoes were considered contemptible. Entering a holy place with shoes is forbidden by the Torah (see Shemot 3:5, among other places). Striking someone with a shoe, or throwing a shoe at someone, was a form of great insult (see Tehillim 60:10). Thus, removing someone’s shoes for them was something that only a slave would be asked to do.
Wearing tefillin, however, is the antithesis of this. Aside from being a positive commandment in which slaves are not obligated, tefillin also are considered to have a unique element of honor attached to them. For example, the passage in Yehezkel (24:17) where the prophet is commanded to continue wearing his glory on his head is understood by the Sages to refer to tefillin.