The Gemara in Masekhet Arakhin (16) comments that the me’il, the robe worn by the kohen, serves to atone for the sin of lashon ha-ra – negative and offensive speech about other people. The basis of this connection is the bells which ran along the bottom of the me’il and produced a ringing sound as the kohen gadol walked. The Gemara comments that the sound produced by the me’il serves to atone for the sin which is violated through sound – namely, lashon ha-ra.
Based on the Gemara’s remark, the Chafetz Chayim, in his famous work on the topic of lashon ha-ra (2:15), associates various aspects of the me’il with the vitally important obligation of shemirat ha-lashon – refraining from negative speech about others. One such aspect is the safa, or binding, which was stitched onto the me’il around the neck. The Torah (Shemot 28:32, 39:23) instructs that the binding should resemble that of a “tachra,” which Rashi explains to mean an armored coat. Surprisingly, the Torah commanded that the me’il, one of the garments worn by the kohen gadol in the Beit Ha-mikdash, should have the appearance of armor worn by warriors in battle. The Chafetz Chayim explained that symbolically, this association between the me’il and armor signifies the protective effect of avoiding lashon ha-ra. The more a person speaks negatively and offensively to and about other people, the more resentment he evokes and the more hostility he invites upon himself. The me’il, which represents the antidote, as it were, to lashon ha-ra, thus resembles a coat of armor, as avoiding lashon ha-ra helps shield us from other people’s hostility.
The Chafetz Chayim speaks in this context specifically of one who finds himself in a quarrel or disagreement with another person. The way to protect himself from the other person’s hostility, the Chafetz Chayim writes, is through silence. The natural instinct is to launch verbal attacks against one’s adversary and try and knock him down, but more often than not, this only backfires and further fuels the flames of acrimony. The Chafetz Chayim urges us to protect ourselves from unnecessary conflicts and tension through shemirat ha-lashon, by exercising restraint and keeping silent even when our instincts tell us to speak negatively and disdainfully about others.