yavat sanjayate kincit
sattvam sthavara-jangamam
tad viddhi bharatarsabha

"O chief of the Bharatas, know that whatever you see in existence, both the moving and the nonmoving, is only a combination of the field of activities and the knower of the field."

Bharatarishabha = Bull of Bharata dynasty [Arjuna], tad viddhi = understand this. Sri Krishna tells Arjuna that atman is imprisoned in a body due to past Karma. The Lord wants atman to be viewed separately from the body. Why we are unable to see atman separately? We are easily confused that atman and body are same. This confusion is in great scholars also. Why so? It is replied in this sloka. Both - soul and body- are bonded intimately. It is like fastening two things tightly and with many knots. One can not easily separate them! Atman and body are bonded by rope Karma, tightly! First we should understand that our atman and body are bonded, we have to loosen the bond and then view both separately. Yavat = whichever, sattvam = living being, sanjayate = is born [and dies]. Stavara - jangama = [living beings are] stationary and movable. Kshetra = body, kshetrajna = atman, samyogat = bondage. How these two are bonded? In the womb of a mother, body slowly graces and an atman is bonded inside. How this atman entered this body? It is because of Karma. We have to realize that atman and body are different; but this knowledge is hidden by Karma. Bondage of these two results in birth; and separation, in death. Karma prevents atman going straight to Moksham, on separation.