Not many of us live in monasteries today and modern life seldom permits us to suddenly stop speaking to those around us. But that doesn't mean we can't avail ourselves of the time-honored benefit of the vow of silence.
Monastic traditions of both the East and West have used the vow of silence to help practitioners achieve greater peace of mind. It proves to be an effective meditation tool because once practitioners quiet the stream of spoken words, it is that much easier to stop the stream of the inner voice. Speaking requires us to think in words, of course, and once we take a sincere vow to stop speaking, we find it easier to still the habitual "thinking in words" that typically disrupts our meditation practice of quieting the mind.
Communicating with our fellow human beings is of such importance to our survival as social beings that the emphasis placed on learning language drives much of our conscious upbringing. Learning to name things, imitating the speech of those closest to us--it is easy to forget how big a part this played in our lives. And because so much of our learned sense of self is determined by our social identity, it is easy to forget the original sense of self, in all its potential, that existed before we learned to think in words.
This contrast between the original and learned sense of self helps meditators experience the difference between Being and Thinking. Where Thinking comprises a linear, time-bound, string of words, Being is a spatial, all-at-once, awareness without words. Because there can be Being without Thinking but not Thinking without Being, we know that Being is fundamental to our nature and that Thinking is acquired through the socialization process. Nearly all meditation techniques aimed at quieting the mind are part of this practice of stopping Thinking in order to return to Being.
Fortunately, we don't need to stop speaking to others in order to stop talking to ourselves and return to the primary experience of Being. All that is really needed is to take a sincere vow of silence at the beginning of each meditation session. This inner vow of silence does not, of course, in and of itself automatically stop habit thoughts from arising -- but it is a perfectly useful and effective way to cut them short.
As each though arises, simply respond by reminding yourself, I'm keeping my vow of silence. This simple technique allows us to step back into Witness awareness and quiet the habit mind instead of following the same old thoughts to the same old conclusions again and again. I'm keeping my vow of silence becomes the thought that stills the Thinking mind and returns us to the presence of Being. It is a practical application of Zen Master Dogen's admonition to Think Not Thinking.
As with all meditation practices, the goal is to bring the peace of mind we find in meditation into the moment-to-moment experience of everyday life. Keeping the vow of inner silence when "sitting, standing, walking and lying down" becomes second nature over time, allowing us to dwell in the calm of Being whenever we are not required by circumstances to step out into Thinking. As with its many allied meditation techniques, the inner vow of silence establishes a spontaneous, enlivened mind that responds to events with compassion and wisdom.