Bhagwad Gita - Post 162

Verse 3

Kshetrajnam chaapi maam

Viddhi sarvakshetreshu bhaarata;

Kshetrakshetrajnayor jnaanam

Yattat jnaanam matam mama.

Do thou also know Me as the Knower of the Field in all fields, O Arjuna! Knowledge of both the Field and the Knower of the Field is considered by Me to be the knowledge.

Sri Krishna says, " I AM THE KNOWER-OF-THE-FIELD IN ALL FIELDS. " If, in all "Fields" the "Knower" is one, then the plurality is only in the matter-envelopments, and the Life that presides over them is one everywhere. 

This Universal One, the Transcendental Truth is indicated here by the first person singular "I AM" because every seeker has to rediscover in himself, "THAT I AM" (Soham).

Lord Krishna is expounding the Gita in a rare moment of Yogic integration. He is identifying himself with the Self that is everywhere. This is something like electricity declaring: "I am the one energy that gives the glow in all filaments all over the world."

Kṣetrajñaṁ cāpi māṁ viddhi sarvakṣetreṣu 

This root of the Being of individuals, of personalities, of things in the world, is sometimes designated as the kshetrajña in us. 

Where is this kshetrajña, the regulator of the kshetra, the operator of this body, the vitality behind all forms in creation? 

Sarvakṣetreṣu bhārata

“I am present as the kṣhetrajña, or the Knower of the field, in all the fields. That is, all individuals whatsoever—right from Brahma, the Creator, down to the atom—are indwelt by Me, and I know all things as the Omniscient Knower.”

When it is our kshetrajna, it is also the kshetrajna of all other kshetras – sarvakshetresu. 

Kshetrajnam mam viddhi

This is something which is not visible to our eyes or palpable to our senses, but the most essential of all essentials in our life.

As inferred in the Vedic scripture Chandogya Upanishad VI.VIII.VII with the aphorism: sa atma tattvamasi meaning Thou art that.  

Knowledge of the kshetra or the physical body and kshetrajna the Consciousness  or eternal soul, is being praised to emphasize its importance. 

Love.