Some recensions (and the Gītā Press text) open the chapter with Arjuna’s question — “prakṛtiṃ puruṣaṃ caiva, kṣetraṃ kṣetrajñam eva ca…” — “I wish to know Prakṛti and Puruṣa, the field and its knower, the means-of-knowledge and the to-be-known.” Other recensions lack it, which is why it is a “hidden” or disputed verse. Whether spoken by Arjuna or implied, it frames the whole chapter as an answer to one deep enquiry: how are these pairs — Nature and Spirit, the field and its witness, the knowing and the known — actually distinct? The entire adhyāya is the reply.

“This body, Arjuna, is called the field (kṣetra); and he who knows it, the sages call the knower of the field (kṣetrajña).” Then the master-key (13.2): “And know Me too as the knower of the field, in all fields.” The definitions are exact. The “field” is everything that can be observed — not only the gross body but the mind and intellect (which, recall from 7.4, are Prakṛti, not the Self). The “knower” is that to which all this is observed, the light of awareness. And this knower, in every body, is one — is “Me”. The whole of Vedānta is folded into this single distinction: you are not the field; you are that which knows it.