Chapter 13, Verse 2
Part of 13: Kṣhetra Kṣhetrajña Vibhāg Yog — क्षेत्र-क्षेत्रज्ञविभागयोगश्री भगवानुवाचइदं शरीरं कौन्तेय क्षेत्रमित्यभिधीयते।एतद्यो वेत्ति तं प्राहुः क्षेत्रज्ञ इति तद्विदः॥
śhrī-bhagavān uvācha idaṁ śharīraṁ kaunteya kṣhetram ity abhidhīyate etad yo vetti taṁ prāhuḥ kṣhetra-jña iti tad-vidaḥ
The Blessed Lord said, "O Arjuna, this body is called the field; he who knows it is called the knower of the field by those who know them."
Kshetra literally means field. The body is so called because the fruits (harvest) of actions in the form of pleasure and pain are reaped in it as in a field. The physical, the mental and the causal bodies go to constitute the totality of the field. It is not the physical body alone that forms the field. He who knows the field and he who beholds it as distinct from himself through knowledge is the knower of the field or matter. Those who know them The sages.