Sosan, also known as the Third Zen Patriarch, played a significant role in the lineage of Zen masters. He was a Chinese Zen teacher who lived during the 7th century and is considered one of the most influential figures in the history of Zen Buddhism.

One of the main contributions of Sosan in the lineage of Zen masters was his role in shaping the teachings of Zen and spreading it throughout China. He was a disciple of the Second Zen Patriarch, Huike, and was chosen by him to be his successor. Sosan continued the teachings of his master and further developed them, making them more accessible to the common people. He wrote several important texts, including the "Hsin Hsin Ming" or "Verses on the Faith-Mind," which is considered one of the fundamental texts of Zen Buddhism.

Sosan's teachings emphasized the concept of "sudden enlightenment," which is the idea that enlightenment can be achieved in a single moment of realization rather than through a gradual process. This concept became a fundamental principle in Zen Buddhism and is still taught by Zen masters today. Sosan also stressed the importance of meditation and mindfulness in achieving enlightenment, and his teachings focused on practical methods to help individuals reach a state of awakening.

Another significant role of Sosan in the lineage of Zen masters was his role in the transmission of Zen to other countries. He is believed to have traveled to Korea, where he transmitted the teachings of Zen to the Korean monk Eka, who later became the founder of the Korean Jogye Order. Through this transmission, Zen spread to other countries in East Asia, including Japan, where it became known as Zen.

Sosan's teachings and influence also had a profound impact on the development of other schools of Buddhism, such as the Pure Land and Tendai schools. His emphasis on the direct experience of enlightenment and the importance of meditation influenced the practices of these schools and helped shape the overall landscape of Buddhism in East Asia.

In conclusion, Sosan's role in the lineage of Zen masters was crucial in the development and spread of Zen Buddhism. His teachings and writings continue to be a source of inspiration and guidance for Zen practitioners around the world. He is remembered as a great Zen master who played a significant role in shaping the history of Zen and Buddhism as a whole.