• The Pele Yo'etz (Sanegoriya) says, "...everything that a man speaks makes an impression and awakens the hosts of Heaven. If one speaks derogatorily, he awakens the prosecuting angels. However, if one speaks in a positive manner, he awakens angels of advocacy. A mans words bear fruit!" (Sparkling Speech by Rabbi Elysha Sandler, page 47)
• "G-d fixed a creative power in the mouths of human beings which resembles His own power of speech. When a person speaks, his words creates spiritual forces" (Sefer Yetzirah 2:6)
• The Chochmas Anach (Parshas Mattos) says,
"'He shall not desecrate his word; according to what comes out of his mouth he shall do' (Bamidbar 30:3). The Chida (Rav Chaim Yosef David Azulai) writes: This posuk alludes to a person who guards his mouth from speaking forbidden words, as well as from engaging in empty talk and sanctifies his mouth. Whatever he requests of Hashem will be accepted. The posuk is interpreted thus: He shall not desecrate his word - if his words are not mundane, in that he does not speak empty words and certainly not words which are forbidden, then whatever comes out of his mouth Hashem will do, and his
prayers will be accepted. Furthermore, even when not in the form of a prayer, whatever he speaks will be fulfilled"
(Sparkling Speech by Rabbi Elysha Sandler, pages 49 - 50)
• Every word a man utters rises upward, splitting heavens to reach its destined place (Nefesh HaChayim 1:13)
A man came to Rav Chaim and asked for a blessing on behalf of his sick mother. Rav
Chaim blessed her with a complete recovery. The visitor was not satisfied with this and said, “I cannot bear to see my mother suffer; I am willing to accept my mother’s sickness upon myself if she will only recovery.”
Rav Chaim reacted strongly. “Do not speak like that! Say, rather, that you will study
Torah on her behalf.”
As soon as this visitor left, a man entered Rav Chaim’s study with dark circles under his eyes from lack of sleep and stress.
He told the following tale. “Last week, I wanted to take a day off from work. With no way to convince my boss to let me off, I told him that my grandmother had passed away suddenly. He graciously granted me a day off. Two days later, my grandmother, who had been completely
healthy, suddenly passed away! Since then I have had no rest. Did I cause my grandmother’s death?"
Rav Chaim spoke to him severely. “You acted extremely foolishly. Chazal teach [Mo’ed
Katan 18a. See also Berachos 19a and 60a as well as Artscroll Sotah 42b, note 10] that ‘a covenant is formed with the lips’: the words that a person says can have a
profound effect and therefore a person must be exceedingly careful about what he says. Now, you should study Mishnayos for your grandmother’s soul for the next year, and with this Hashem will help you.”
The man left and Rav Chaim turned to his family members who were in the room.
“Where is the man who said he would accept his mother’s illness? Tell him to ask this person how careful a person must be with his speech!” (Rav Chaim Kanievsky on the Three Weeks by Rabbi Avraham Yeshayahu Shteinman, pages 220 – 221. See also See Sparkling Speech by Rabbi Elysha Sandler, pages 46 – 50, for more on this subject)