One day Yao-shan Wei-yen (750-834), one of the well-known Chinese Ch'an master, was asked by the host of the monastery to give his sermon to the assembly who for a long while was expecting his teaching. Yao-shan said: "Strike the bell."
A breath is a moment in time. There is no past and no future. A breath is like the refresh button on your computer. It clears the past screens and you start over in your Buddha nature. Somewhere in the guts of your machine the past karma lingers but it has nothing to do with you. As you follow your breath it is a space-time continuum; it has no mass but it has a rhythm. mu