Once upon a time, in a certain town there was a coffin maker who opened and was running a store where he sold the coffins he made himself to the customers in the neighborhood. The popuplation in the town increased day-by-day.
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