The greatness of its power for good, and the opposite, God forbid.
1. Poverty comes through lashon hara and idle talk, but through [giving] charity to a Torah scholar, this is fixed and one merits wealth. (From Likutei Moharan I, 4)
2. By speaking out Torah in words, the speech enlightens the person in all the places he needs to repent, until he merits complete repentance. By this, one merits to come to understandings of the Torah in its depth (see sec. Torah Learning, #1-11). (From Likutei Moharan I, 11)
3. Via wholeness of holy tongue, meaning holiness of speech, wherein one increases speaking words of Torah, prayer, supplications, requests, and conversations between himself and his Creator, and he is careful not to speak defective words which include lashon hara, lies, etc - through this [holiness of speech] one merits tikun habrit. Also, to the opposite: through tikun habrit one merits wholeness of holy speech. (From Likutei Moharan I, 19)
4. Speech that isn't listened to and received isn't called speech at all. The rectification for speech, that it will be listened to and received, is through praise of the true tzadikim - this is [in fact] the overall rectification of speech. (From Likutei Moharan I, 29)
5. Words are the vessels of abundance [from HaShem]; abundance is received by them. According to speech, thus is the abundance [received] - if speech is whole and in its fullness [in holiness], then one can receive much abundance through it. For this reason is it necessary to speak prayer [and not merely think it]. (From Likutei Moharan I, 34)
6. When one blemishes speech, which is the breath of the mouth of the Holy One Blessed is He, then through the blemish, the breath (ruah) of his mouth is made into a storm wind (ruah). The storm wind is the great Accuser, that from him come all the prosecutions and tests [that a person goes through], and he "assaults the bodies of human beings" (Tikunei HaZohar, Tikun 18). All the bad informing (tattling) that people speak about a person comes from this storm wind, because it is the aspect of "the end of all flesh" (Genesis 6), since he makes an end and finality to all flesh. All of this comes from a blemish in speech. (From Likutei Moharan I, 38)
7. The rectification of speech is through the Torah learned in poverty and hardship at a time when a person is pressed. A cord of mercy is drawn over a person from this, and all prosecutors and the whole side of impurity (evil forces) are banished from him. [Also] through this, speech is rectified and elevated to it's source. Then, the speech comes out in song, praise, and glorification of the Holy One Blessed is He, [and one] merits to to pray to, thank, and praise HaShem. By this, one will merit to speak between himself and his Creator with a blaze of power, arousing himself to [true] service of HaShem, until he'll merit to true speech - to the choicest truth within the speech, meaning he'll speak before HaShem in great and full truth, and he'll spread out his conversation and speak with the heat (passion) of the heart words of truth within the heart, with great arousal to repentance, until he'll see his [own] insignificance and the greatness of the Creator until he comes to great shame from this, becoming ashamed from before Him over the greatness of his sins.
Through this, one merits the light of tefillin, which are an aspect of devekut to HaShem, the aspect of the radiating skin of the face (Exodus 34). By [attaining all of] this, all of one's transgressions are forgiven and one clings himself to the Tree of Life (see Shame and Brazenness, #2). (There^)
8. One must be careful not to hear words from a knowledgeable wicked person because his words are venomous air of promiscuity and they give birth to promiscuity in the listener. (From Likutei Moharan I, 43)
9. Words that are not holy words, cause the awakening of the sukot of the Christians, the suka of the nations of the world, and the right hand of falsehood overpowers, the exile increases, and [the Jewish people] is distanced from the holiness of the Land of Israel. And [also] through this, the Rabbi of truth is ignored, and conflict and dispute increase, and the Divine Presence comes into dispute with her children (Israel) in exile (Tikunei HaZohar) who had been exiled from their Father's table and had left their Land.
However, through holy speech, which is powerful prayer, the truth overcomes (see sec. Prayer, #45). (From Likutei Moharan I, 48)