In terms of psychological symbolism, it expresses the union of opposites—the union of the personal, temporal world of the ego with the non-personal, timeless world of the non-ego. Ultimately, this union is the fulfillment and goal of all religions: It is the union of the soul with God.
Jung defines the union of opposites as the supreme psychological and religious achievement, equating it with the soul’s unification with the divine and the integration of ego with the transpersonal Self.
, Man and His Symbols, 1964thesis