One Who Keeps His Word Has Power in His Mouth:
The pasuk (Devarim 17:6) states: “According to the words of two witnesses (eidim) or according to the words of three witnesses, the matter shall stand (yakum davar).” Sefer Ahavas Shalom writes that the word “eidim” can also be translated to mean “signs”, while the word “davar” can also mean “words” (dibbur). Accordingly, the pasuk can be understood to be saying that there are two signs upon which one’s words stand. During the week, these signs are bris milah and tefillin. On Shabbos, the signs are bris milah and the day of Shabbos itself (as is stated in the introduction to the Zohar Hakadosh).
In other words, one’s words will be accepted and influential if he has these signs. This is as is stated in Chazal (Brachos 6B): “If one has yiras shomayim, his words will be heard” – both in this world and in the Upper Worlds, and he will even have the power to use his words to annul Divine decrees (see Rashi, Moed Koton 16B). However, if one does not uphold these signs, his words are “sickly’ and have no power.
With this in mind, he explains the pasuk to be saying: “Lo yachel devaro” – he should not make his words sick (choleh). If one keeps his word, his words will have power to change things in this world and in the Upper Worlds. But if one doesn’t, his words are sickly and unable to accomplish anything.
