Parshat Matot begins by describing the different kinds of vows a person can make, and how to annul them. It also says that, one, a person should not go back on his words, and two, a person should perform everything that leaves his mouth.
Why does the Torah have to say both the positive of doing everything that leaves his mouth, and also the negative of not going back on his words? Commentaries point out that the Torah is elevating a person’s words and turning them into a commandment, as if his words were biblical. They describe how we are above animals because we can speak, and we should use that power wisely.
They also point out that speech really is a power, able to raise and lower people’s spirits. Some commentaries have even pointed out how we have two eyes, two ears, and two nostrils, but only one mouth, proving that one mouth can do damage or cause good like two of any of the other body parts.
But there is something else that can be used to symbolize the power of speech. Our mouths have sharp teeth, but have soft lips to protect us from exposing those teeth. We may have bad things to say, but we have to use our lips to prevent ourselves from speaking negatively. But we have a tongue, which is also soft! Maybe we should learn to protect our insides from thinking negatively about others, so that we will not have to come to use external measures not to say them! It all starts from the inside. The Torah is urging all of us to improve our lives from our insides, and improve someone else’s life with our outsides. The Torah also teaches us that we should watch what comes out of our mouths, and not violate the negative of going back on our words.