The "Rinzai Roku" is a collection of recorded sayings and teachings of the founder of Rinzai Zen, Linji Yixuan. It serves as an important text and guide for practitioners of Rinzai Zen, including Hakuin Ekaku.

In Rinzai Zen, the "Rinzai Roku" plays a crucial role in transmitting the teachings and methods of the school. It is considered a primary source of wisdom and guidance for practitioners, providing them with a roadmap for their spiritual journey.

One of the key teachings of the "Rinzai Roku" is the concept of "kensho," or sudden enlightenment. This is the idea that one can achieve enlightenment in a single moment of insight, rather than through gradual practice and accumulation of knowledge. This concept is central to Rinzai Zen and is reflected in the teachings and practices of Hakuin Ekaku.

The "Rinzai Roku" also emphasizes the importance of "koans" in Rinzai Zen practice. Koans are paradoxical or nonsensical statements or questions that are used to challenge and disrupt the rational mind and lead to a deeper understanding of reality. Hakuin Ekaku was known for his skill in using koans to guide his students towards enlightenment.

In addition to these teachings, the "Rinzai Roku" also includes practical instructions for meditation and other practices, as well as anecdotes and stories from the lives of Zen masters. These serve as examples and inspiration for practitioners, showing them the potential of achieving enlightenment and the dedication and discipline required to do so.

Overall, the "Rinzai Roku" serves as a foundational text for Rinzai Zen, providing practitioners with a framework for understanding the teachings and methods of the school. It continues to be studied and revered by practitioners, including Hakuin Ekaku, who saw it as a valuable tool for guiding students on their spiritual path towards enlightenment.