Mark Nepo writes in The Book of Awakening:
It is amazing to consider how as infants we are one with everything. In time, of course, we learn how to distinguish between ourselves and others, between the world we carry inside and the world we move through. But ironically, the sages of all paths are those who, after lifetimes of experience, try to return to this primary state of Oneness.
When I think of the moments I have felt most alive, they all have the quality of joining all-of-what-I-keep-inside with everything-outside-me in a way that makes me forget myself. They all feel timeless and open-ended. Tenderly, the deepest moments of making love allow us to join in that Oneness beyond ourselves, as do certain moments of being immersed in great music or great open spaces. I have also felt this after long periods of swimming or running, or after long periods of being healthfully alone. I feel it when discovering what it is I need to write. Joy, it seems, is the feeling of that Oneness.
Not surprisingly, it is the risk to love—the risk to give our full attention—that lets what-is-eternal-within merge with what-is-eternal-without. In those moments of Oneness, we, as drops of spirit, join the larger river of spirit.
From The Book of Awakening by Mark Nepo