Why Doesn't the Buddha Go to the Formless Realm to Teach the Dharma

Beings in the formless realm have no bodies, yet they have consciousness; where there is consciousness, there is the aggregate of consciousness (vijñāna). Although they have consciousness, they cannot hear the Buddha's Dharma, much less contemplate it. Having no body, they are not humans in the human world, yet they are beings of the heavenly realms—higher forms of life. Feeling, perception, and formations—the five universally present mental factors (sarvatraga)—are present in all eight consciousnesses. Formless-realm devas also have the feeling, perception, and formations of the mind consciousness, as well as the feeling, perception, and formations of the manas, and also the feeling, perception, and formations of the eighth consciousness.

The Buddha could teach the Dharma to the devas in the formless realm, but the devas of the form realm could not hear it, humans in the human world could not hear it, and ghosts and spirits could not hear it. Beings in the formless realm are so few, and they are all non-Buddhists who spend their days absorbed in meditation, so there is no need at all to teach them the Dharma. From another perspective, once one reaches the dhyāna of the second absorption, one can no longer hear the Dharma; how much less can one hear and contemplate the Dharma in the dhyānas of the fourth absorption and above. Therefore the Buddha does not go to the formless realm to teach the Dharma.

One can enter the dhyāna of the second absorption in a single instant, and then know nothing at all; emerging from it also takes just an instant. Only after emerging does one realize that one had just been in meditative absorption, feeling the body to be extremely comfortable, the mind especially joyful, and the head particularly clear. A faint sound is enough to awaken the ear consciousness, and thus one emerges from absorption. Because the manas still has matters it is concerned about, when the time comes, if someone reminds one of an important matter—even the sound of a mosquito—one can hear it, and thus emerge from absorption. Before entering absorption, amid very noisy sounds, the mind can quickly settle down; the noisy sounds grow fainter and fainter, and then can no longer be heard, and one enters absorption.

The Buddha taught the Huayan Sutra and the Kṣitigarbha Sutra in the desire realm and the form realm heavens, and they were then transmitted to the human world. The other sūtras were all taught in the human world, so that devas could descend to hear the Dharma, and ghosts, spirits, and animals could also hear the Dharma; in this way more sentient beings were delivered.