Sosan, known as the Third Patriarch of Chan, shaped the later unfolding of Zen primarily through the text traditionally attributed to him, the *Xinxin Ming* (*Hsin Hsin Ming*, often rendered “Faith in Mind” or “Verses on Faith-Mind”). This early Chan poem articulates a radical non-dualism: the unity of apparent opposites, the futility of discriminating thought, and the call to relinquish preference. Its famous insistence that the Great Way is not difficult for those who do not cling to likes and dislikes became a touchstone for later Zen, setting a tone that is wary of doctrinal fixation and conceptual elaboration. The poem’s language of suchness—reality as it is, free from fixed attributes—encouraged a direct, unmediated encounter with experience rather than reliance on intellectual analysis. In this way, Sosan’s teaching offered a concise doctrinal matrix within which later Zen traditions could recognize their own essential orientation.

Within East Asia, this influence unfolded through both lineage and text. In China, Sosan stands in the early patriarchal line that shaped the atmosphere inherited by later Chan masters, whose systematization of meditation and monastic life unfolded within the non-discriminative, non-dual vision articulated in *Xinxin Ming*. As Chan moved to Japan, this vision became integral to both Sōtō and Rinzai Zen: the Sōtō emphasis on “just sitting” resonates with the poem’s call for effortless, non-striving awareness, while Rinzai’s stress on spontaneity and cutting through dualistic thinking finds support in its stark, paradoxical statements. Across these schools, the text came to be studied, chanted, and commented upon, functioning as a kind of distilled guide to the Zen understanding of mind.

A similar pattern can be seen in Korea and Vietnam, where Chinese Chan lineages and scriptures were transmitted and assimilated. In Korean Seon, Sosan’s non-dual, non-discriminating approach harmonized with an emphasis on sudden enlightenment and the integration of meditative insight with ordinary activities. Vietnamese Thiền likewise drew on teachings of effortless awareness and non-attachment that accord with the practical, liberation-oriented character of its Buddhism. In these various cultural settings, *Xinxin Ming* served not merely as a text to be read, but as a mirror for practice: it shaped how practitioners understood mind as inherently Buddha, how they approached meditation without forcing or striving, and how they trusted the Way that is already present when grasping and aversion fall away.