Upon examining the text, the end of the pasuk seems redundant. Would it not have sufficed to simply write, “You shall observe and carry out whatever emerges from your lips.” Horav Mordechai Rogov, zl, makes a practical insight which explains the pasuk. When a person is involved in an “eis tzarah,” a period of pain or anguish, the neder, vow, which he makes is undoubtedly sincere. He is stressed and motivated by anxiety. At the time, he truly plans to fulfill every promise that he makes. What happens, however, when it is all over and things have calmed down, when there is no longer a reason to worry? Does he retain the same genuine feelings as he had before, or is he doing what he has to do because he committed himself during his time of need? The Torah demands that an individual demonstrate the same enthusiasm when fulfilling his promise, as when he had originally made the vow.
David Hamelech says in Tehillim 116, “My vows to Hashem I will pay, in the presence, now, of His entire People.” What is so impressive about David’s fulfilling his vows? Is that not to be expected? Horav Rogov suggests that David is saying he will fulfill his vows with the same enthusiasm and emotion that he exhibited when he originally made the vow. This is the interpretation of the pasuk, “You shall observe and carry out what emerges from your mouth” – fulfill your requirements not out of obligation and complacency, but – “just as you vowed... whatever you spoke with your mouth.” With the exact conviction, with the same sentiment with which you made the vow, so should you fulfill its demand.
