The Medrash tells us in regards to the words in the parsha:
לֹא יַחֵל דְּבָרוֹ (במדבר ל:ג)
(he should not profane his word). This obligation applies to Jews and not to Gentiles. In fact, much of the laws of vows are oriented towards Jews and not towards Gentiles. Why should it be that this ability to consecrate something verbally was given only to Jews?
The purpose of the mouth is to praise G-d through Torah and Mitzvos. The Navi says:
עַם זוּ יָצַרְתִּי לִי, תְּהִלָּתִי יְסַפֵּרוּ. (ישעיהו פרק מג:כא)
The people which I formed for Myself, that they tell of My praise (and not a Gentile).
Being that this is so, this power was given to the Jews for their utterances and not to the Gentiles. The Yerushalmi explains that on a theoretical level, even permitted speech that is mundane should not be uttered with the mouth used for the service of Hashem. Instead we should have a “separate mouth”, in order not to defile our “holy mouth” – the mouth used for the service of Hashem.
That “separate mouth” is the mouth that we share with the Gentiles. But the “holy mouth” is unique to the Jew. In light of this we can understand the Orach Chaim in last week’s parsha. He tells us that the mouth is a cli shares (“A holy vessel”) for the service of Hashem. The mouth has the power to infuse words with holiness, thus giving them new implication.
The Shlah Hakadosh, in this week’s parsha, tells us that ״לא יחל דברו״ includes keeping one’s word even when one didn’t make a vow and even when one has no legal obligation to keep it. Obviously, not keeping one’s word brings anguish to those who were counting on him. The Shlah, however, is telling us that you are actually damaging yourself as well. Your holy mouth has become mundane, thus weakening your Torah and Tefillah.
It is obvious at this time of year when we work on our relationships with other people, that we have to be careful about the way that we speak. Many times I am approached by people that want to “get out of” a promise. For example, they made a verbal commitment to a friend, neighbor or client, and now want to retract the commitment. This person even reminds me that there was no formal agreement made—certainly nothing that would be binding in a court of law! However, the Shla Hakodesh tells us that retracting these non-binding words would be included in lo yachel devoro.
During these weeks, when we try to improve our speech and certainly not to hurt others with it, we many times focus on insults, loshen hara and the like. This year aside from those major infractions, let us focus on keeping our word, which not only negatively affects our friend, but it dilutes and impacts the power of our holy speech, weakening our Torah and Tefillah as well.