The question of why it should be some important for Jews to make void a spoken vow requires some background of the nature of vows.
The Torah teaches us that Israelites could make vows to bring a sacrifice to the Temple. Breaking such a vow was unthinkable, it was a promise made to God.
People made vows to do all kinds of things that did not concern the Temple, yet the vows were still considered to be a promise made before God. The Rabbis argue over whether it was possible to break a vow once it was made. They concluded that there were few occasion when a vow could be broken.
The form of a vow, though formal, could be a simple declarative statement, without actually referring to God. A sentence such as "I will never again go to such an such a place, was considered a form of a vow, that is, a promise made before God.
Such a strong emphasis on the spoken word is unusual. It indicates another way of thinking about the significance of language. ANYTHING that one says, whether said thoughtlessly or in anger, was absolutely binding on an individual. There was no such thing as idle words. Saying to a friend or spouse in anger, "I will never speak with you again," could have disastrous consequences.
It is no small wonder that the Jews who were forced to submit to conversion were concerned about what they had said. They had been taught to consider seriously every oath they made.
This way of using language is still adhered to in certain circles. A good portion of the worlds diamond trade is centered din New York, and many of the brokers are Orthodox, Hasidic Jews. Written contracts are not used. A persons word is the basis of a deal which may involve thousands or millions of dollars.
By contrast, how do we use our words. How seriously do we mean what we say ? How often do we let words fly off our tongues without even thinking ? How often do we speak half truths, because it is easier that speaking the whole truth ? How often do we say something in anger, then after we have cooled of, apologize by saying that we did not mean what we said ? How often do we say something, and than forget what we said ?
Have we made pledges to be better Jew, and forgotten ? Have we vowed to give to Tzedakah and forgotten ? Have we pledged to support the Synagogue, and neglected to follow up on those words. Do we merely pay lip service to the words that we recite during the High Holidays once they have passed ? Do we say things to appease our spouse, children, parents or friends, without ever intending to do what we say.
The results of our attitude towards what we say has been to cheapen the value of the spoken word. If words are not spoke seriously, they are not listened to seriously. This diminishes our ability to communicate. When we are serious about what we say, know one believes us, like the child who cried wolf once too often.
On this Yom Kippur, let us consider carefully the value of our words. Instead of speaking half truths, let us speak the whole truth, no matter how painful. When we say something, let us make up our minds to fulfill what we have promised. Instead of speaking simply for the sake of hearing words come out of our mouths, let us weigh our words with care. Let us think before we speak. Once we have spoken, let those words become our pledge.
Speech is that which sets humans beings apart from animals. Can we afford to use this priceless gift in the way we do ? I think not.
May the words of our mouths,
And the mediations of our hearts, be sincere before You,
O God, our Rock and Redeemer