Hakuin Ekaku, also known as Hakuin Zenji, was a famous Japanese Zen master who lived during the Edo period. He is considered to be the reviver of Rinzai Zen, one of the three main branches of Zen Buddhism. Hakuin's teachings emphasized the importance of rigorous meditation practice and the realization of one's true nature.

One of the key teachings of Hakuin was the practice of "koan," a paradoxical question or statement that is used to challenge the student's logical thinking and bring them closer to enlightenment. Hakuin believed that through the intense contemplation of koans, one could break through the limitations of the rational mind and experience a direct understanding of reality.

Hakuin also emphasized the importance of "zazen," or seated meditation, as a means to cultivate mindfulness and awareness. He taught that through zazen, one could quiet the mind and let go of distractions, leading to a deeper understanding of the true nature of existence.

Another important aspect of Hakuin's teachings was the concept of "kensho," or sudden enlightenment. He believed that through intense meditation and contemplation, one could experience a sudden and profound realization of their true nature. This experience was often described as a moment of clarity and understanding that transcended words and concepts.

Hakuin also emphasized the importance of ethical conduct and moral discipline in the path to enlightenment. He believed that one must cultivate virtues such as compassion, wisdom, and humility in order to progress on the spiritual path.

In addition to these teachings, Hakuin also emphasized the importance of a close relationship between a student and a teacher. He believed that a skilled teacher could guide the student on the path to enlightenment and help them overcome any obstacles they may encounter.

Overall, Hakuin's teachings focused on the importance of rigorous meditation practice, the realization of one's true nature, and the cultivation of ethical conduct. He believed that through these practices, one could break through the limitations of the ego and experience a profound understanding of reality. His teachings continue to influence Zen practitioners around the world and his legacy as the reviver of Rinzai Zen remains strong.