The "Hakuin Zenji Zazen Wasan" is a collection of 100 verses composed by Hakuin Ekaku, a prominent figure in the revival of Rinzai Zen in Japan during the Edo period. These verses were meant to be recited during zazen, the seated meditation practice central to Rinzai Zen.

The word "wasan" can be translated as "poem of praise" or "hymn of praise," and these verses serve as a way to express gratitude and reverence for the practice of zazen and its benefits. The "Hakuin Zenji Zazen Wasan" is often recited by Rinzai Zen practitioners before and after zazen, as a way to connect with the lineage of masters who have passed down this practice.

In terms of its role in Rinzai Zen, the "Hakuin Zenji Zazen Wasan" serves several purposes. Firstly, it serves as a reminder of the importance of zazen in the Rinzai Zen tradition. Hakuin himself was a fierce advocate of zazen, often saying "zazen is the gate to all the ten thousand treasures." By reciting these verses, practitioners are reminded of the significance of zazen and its potential to lead one towards awakening.

Secondly, the "Hakuin Zenji Zazen Wasan" is a way to pay homage to the lineage of masters who have contributed to the development and preservation of Rinzai Zen. Hakuin himself was a successor of the Rinzai Zen lineage and was deeply indebted to his predecessors. By reciting these verses, practitioners are connecting with the long line of masters who have dedicated their lives to the practice and teachings of Rinzai Zen.

Lastly, the "Hakuin Zenji Zazen Wasan" is a way to cultivate a sense of gratitude and humility within practitioners. The verses express gratitude for the teachings and guidance of the masters, as well as for the opportunity to engage in zazen. This sense of gratitude and humility is an important aspect of Rinzai Zen, as it helps to cultivate a mind free from ego and attachment.

In conclusion, the "Hakuin Zenji Zazen Wasan" is a collection of verses that serves to remind practitioners of the importance of zazen, pay homage to the lineage of masters, and cultivate a sense of gratitude and humility. Its role in Rinzai Zen is integral, as it helps to deepen one's understanding and practice of this tradition.