One who does not exercise proper caution in matters of speech may
find himself inadvertently fanning the flames of hatred. It is
forbidden to mention an incident or other piece of information
which might remind the listener of a situation where he was wronged
by someone. To relate such information is to speak avak (lit., the
dust of) rechilus. The speaker transgresses even though he has no
intent of causing the listener to recall the wrongdoings; the Sages
hold the speaker responsible for not having exercised proper
caution in mentioning that which might reawaken ill feelings.
The following segment is a translation from the Chofetz Chaim's writings on the philosophy of proper speech from the Sefer Shmiras Halashon.
Choose Your CompanyScripture states: "Withdraw yourselves from the man whose life's breath is in
his nostrils, for with what is he deemed worthy?' (Yeshayahu 2:22). Zohar
comments (Parashas Tetzaveh):
With these words, the Holy One, Blessed is He, commands and cautions man to
guard himself from those who have turned away from the path of good to that
of evil, who have contaminated their souls ... And how is man to know whose
company he should seek and whose he should avoid? By gauging an individual's
anger, one can determine what sort of person he is. If when anger comes upon
a person, he guards the sanctity of his soul and does not allow it to be uprooted
and replaced by that "foreign G-d" [that is anger], then he is a person whom
it is fit to be near. However, if he does not guard the sanctity of his soul,
allowing it to become uprooted so that the "other side" can dwell in its place,
surely he is a person who rebels against his Master, and it is forbidden to seek
his company ... He is the person who "tears apart his soul in his anger" (Iyov
18:4); he tears apart and uproots his soul because of his anger, and allows a
foreign G-d to dwell within himself.
Regarding such a person it is written, "Withdraw yourselves from the man
whose life's breath is tiec [lit., in his nostrils]," [meaning,] whose sacred
soul is torn apart and contaminated tiec, by his anger ..1
Thus, it is imperative that one rid his heart of anger so that he will be
saved from Gehinnom and will merit entry into the World to Come.