The first part of the Oniazami is written by Hakuin in the form of a letter to the abbesses Hōkyō-ji Monzeki 寶鏡寺門跡 and Kōshōin Monzeki 光照院門跡, both daughters of Emperor Nakamikado 中御門 (1701-1737).

In 1751 Hakuin spent a period of three months in Kyoto, during which he visited the two imperial abbesses on several occasions to preach at their temples. On those occasions he could not fail to notice how they lived, waited upon by numerous maids and attendant nuns. In his letter Hakuin admonishes the imperial abbesses, criticizing in clear terms their luxurious lifestyles and sumptuous robes, and chiding such lapses as their failure to help with the cleaning (an important part of Zen practice). It was quite an item of conversation in Kyoto at the time that such frank and plainspoken criticism would be directed to members of the imperial household.

Particularly stressed in the Oniazami is the importance of true Zen practice based on dōchū no kufū (“meditation-in-activity”: Zen practice in the midst of work and action). Merely enjoying the stillness of zazen never leads to true samadhi power, Hakuin states. Such power is built only by maintaining a clear state of mindfulness amidst the complex activities of daily life.