People have become convinced that there is a spiritual benefit to living in the present. This is a surprising phenomenon, because nothing seems more mundane than the here and now. You wouldn't expect anything special to emerge from the constant flow of seconds, minutes, and hours that fill everyone's life from the moment of birth. There must be a deeper reason for giving the present moment a special value. (As an introduction to the significance of now, please see my recent post, "What Does It Mean to Live in the Present?"
"Now" is a concept that runs deeper than you might suppose. First of all, it cannot be measured by the clock. Before the tick of the clock is over, it has vanished into the past. Likewise, the experience of now as a subjective event is ungraspable by the mind. A thought is gone the instant you think it, and there's an argument from neuroscience that says the words you perceive as a thought are after-effects of the brain activity that created them, since the electrical impulses and chemical reactions inside neurons take fractions of a second, while the words in your head take much longer.