Dharma transmission is a crucial aspect of Rinzai Zen, a branch of Zen Buddhism that focuses on the use of koans (paradoxical riddles) and rigorous meditation practices to achieve enlightenment. It is the passing down of the teachings and lineage of the Zen tradition from teacher to student, ensuring the continuity and authenticity of the teachings.

In Rinzai Zen, dharma transmission is seen as a direct transmission of the Buddha's enlightenment through the lineage of masters, dating back to the founder of Rinzai Zen, Linji Yixuan. This transmission is believed to be a transfer of the master's awakened mind and understanding to the student, rather than just the transmission of knowledge or techniques.

Hakuin Ekaku, also known as the "Reviver of Rinzai Zen," was a prominent Zen master who played a crucial role in the revival and spread of Rinzai Zen in Japan during the 18th century. He received dharma transmission from his teacher, Shoju Rojin, who was a disciple of the famous Zen master, Mokuan Shoto. This transmission was a pivotal moment in Hakuin's spiritual journey, as it marked his official recognition as a Zen master and his authorization to teach.

According to Hakuin's own account, his dharma transmission was not a formal ceremony but rather a spontaneous and intimate moment between him and his teacher. One day, while Hakuin was meditating, Rojin approached him and asked him to demonstrate his understanding of a koan. Hakuin's response was so profound and insightful that Rojin immediately recognized him as his successor and transmitted the dharma to him.

However, this was not the only instance of Hakuin receiving dharma transmission. Throughout his life, Hakuin received dharma transmission from several other masters, including his own father, who was also a Zen master. This is because, in Rinzai Zen, dharma transmission is not a one-time event but a continuous process of deepening one's understanding and realization of the teachings.

Hakuin's dharma transmission marked the beginning of his role as a master and teacher, and he went on to train and transmit the dharma to numerous disciples, who in turn spread his teachings throughout Japan. His emphasis on rigorous meditation and the use of koans as a means of attaining enlightenment greatly influenced the development of Rinzai Zen and continues to be a fundamental aspect of the tradition today.

In conclusion, dharma transmission in Rinzai Zen is a crucial aspect of the lineage and transmission of the Buddha's teachings from master to student. Hakuin Ekaku's own transmission was a pivotal moment in his spiritual journey and marked the beginning of his role as a master and teacher, furthering the spread and development of Rinzai Zen.