Bhagavad Gita: Chapter 13, Verse 2

श्रीभगवानुवाच |
इदं शरीरं कौन्तेय क्षेत्रमित्यभिधीयते |
एतद्यो वेत्ति तं प्राहु: क्षेत्रज्ञ इति तद्विद: || 2||

śhrī-bhagavān uvācha
idaṁ śharīraṁ kaunteya kṣhetram ity abhidhīyate
etad yo vetti taṁ prāhuḥ kṣhetra-jña iti tad-vidaḥ

śhrī-bhagavān uvāchathe Supreme Divine Lord said; idamthis; śharīrambody; kaunteyaArjun, the son of Kunti; kṣhetramthe field of activities; itithus; abhidhīyateis termed as; etatthis; yaḥone who; vettiknows; tamthat person; prāhuḥis called; kṣhetra-jñaḥthe knower of the field; itithus; tat-vidaḥthose who discern the truth

shri-bhagavan uvacha
idam shariram kaunteya kshetram ity abhidhiyate
etad yo vetti tam prahuh kshetra-jna iti tad-vidah


BG 13.2: The Supreme Divine Lord said: O Arjun, this body is termed as kṣhetra (the field of activities), and the one who knows this body is called kṣhetrajña (the knower of the field) by the sages who discern the truth about both.


Here, Shree Krishna begins explaining the topic of distinction between the body and spirit.  The soul is divine, and can neither eat, see, smell, hear, taste, nor touch.  It vicariously does all these works through the body-mind-intellect mechanism, which is thus termed as the field of activities.  In modern science, we have terms like “field of energy.”  A magnet has a magnetic field around it, which creates electricity on rapid movement.  An electric charge has a force field around it.  Here, the body is the receptacle for the activities of the individual.  Hence, it is termed as kṣhetra (the field of activities). 

The soul is distinct from the body-mind-intellect mechanism, but forgetful of its divine nature, it identifies with these material entities.  Yet, because it has knowledge of the body, it is called kṣhetrajña (the knower of the field of the body).  This terminology has been given by the self-realized sages, who were transcendentally situated at the platform of the soul, and perceived their distinct identity separate from the body.