The circles (ensō) shown in the two presentations of the ox-herding pictures in D.T. Suzuki's book, Manual of Zen Buddhism illustrate the actualization of non-duality (advaya), the real goal of Zen Buddhism.
The ox-herding pictures are a series of ten images that depict the stages of a practitioner's journey toward enlightenment. These stages range from the initial search for the ox (symbolizing the true self or original nature) to the realization and embodiment of this true nature. The process involves searching, finding, taming, and ultimately transcending both the seeker and the sought, symbolizing the dissolution of duality and the realization of non-duality.
In the final stages of the ox-herding pictures, the man (the seeker) and the ox (the object of the search) disappear. This disappearance represents the dissolution of the ego (I am this carnal body) and the realization that the distinction between the seeker and the sought was illusory. What remains is a state of pure, unbounded radiant awareness, free from the dualistic distinctions that characterized the earlier stages of the journey.
This state of non-dual awareness, whether called the One Mind or Tathata, represents the ultimate goal of Zen practice: to see through the illusion of separation and experience the true nature of reality as a unified whole. This profound insight into the nature of existence aligns with the core teachings of Zen Buddhism and emphasizes the importance of direct, experiential understanding over conceptual knowledge.