Eckhart Tolle’s book, The Power of Now, should be retitled to read, The Power of Samsara, because this is exactly what the now is. Using the analogy of a movie, the now is like one frame of samsara. Whether the now is a frame at a time or an entire movie, the now can never be nirvana.
Truth be told, there is no now when we awaken to our true nature. Such a nature cannot be squeezed into a now. All the nows that have ever been are illusory.
Before we are purified, enough to come to our first initial realization of pure Mind, we must first lose all faith in now, i.e., this moment. It is not enlightenment.
I can remember once when I gave myself up to cleaning out the Zen temple's garden being focused on the here and now as my teacher instructed. Later, I realized that it wasn't any different than when my Zen teacher and I got drunk together on cheap beer (and I mean cheap). The series of nows that made up my life pointed in one direction. It was samsara—not awakening.
Thanks to a few great mentors like Bishop Nippo Shaku, I sought to find the pure essence of my ordinary mind and its thoughts—an essence that was anything but ordinary or now. Looking back to this time from my present vantage point I can say, with absolute surety that, primordially, we are the Buddha-nature or if your like we are the One Mind. Unfortunately, if we don't recognize our Buddha-nature we remain stuck in the nows of suffering and rebirth.
The real path we should be on goes beyond the now or the present moment. This path is about a search for our true nature. I can assure you that if we look hard enough, exhausting every possible avenue, eventually this true nature will discover us exactly when we discover it. There will be mutual recognition followed by what is called the light of Mahayana (mahâyana-prabhâsa).