From the halachic point of view, the making of vows is a major issue. The halachic analyses of the Kol Nidre with which Yom Kippur commences could take up a library (as could the literary and historical aspects of the subject).
The underlying concept is the importance of how you use words. The capacity of speech is one of the great marks of distinction between man and the rest of Creation.
Yes, other species have their means of communication, and Martin Buber points out that even silence is communication. One example is what the English language calls “companionable silence”.
The careless and over-profuse use of words is one of our worst problems. The Midrash quotes the sentence from this parashah, “A person shall not break his word” (Num. 30:8), and goes on, “for one knows not when his time (of death) shall come”. What you say can wreak immense damage, and you might, God forbid, die before you have had a chance to repair what you have done.
There is a saying, “Everyone thought he was a fool, and when he opened his mouth they had their proof”. Being a fool in your speech is bad enough, but it’s worse if you let your words betray a spark of evil.