tat kshetram yac ca yadrk ca
yad-vikari yatas ca yat
sa ca yo yat-prabhavas ca
tat samasena me shrinu
Now please hear My brief description of this field of activity and how it is constituted, what its changes are, whence it is produced, who that knower of the field of activities is, and what his influences are.
Commentary by Srila Prabhupada
The Lord is describing the field of activities and the knower of the field of activities in their constitutional positions. One has to know how this body is constituted, the materials of which this body is made, under whose control this body is working, how the changes are taking place, wherefrom the changes are coming, what the causes are, what the reasons are, what the ultimate goal of the individual soul is, and what the actual form of the individual soul is. One should also know the distinction between the individual living soul and the Supersoul, their different influences, their potentials, etc. One just has to understand this Bhagavad-gita directly from the description given by the Supreme Personality of Godhead, and all this will be clarified. But one should be careful not to consider the Supreme Personality of Godhead in every body to be one with the individual soul, the jiva. This is something like equating the potent and the impotent.
Commentary by Sri Visvanatha Cakravarti Thakur
Now the Lord begins to elaborate on what he has said previously in abbreviated form.
Hear from me in brief of what the body consists (yac ca) - a conglomeration of five gross elements, prana, senses and other things; what qualities it exhibits (yadrk)- such as desire; what its transformations are (yad vikari)–being subject to changes either favorable or unfavorable; from what it arises (yatah)–from the combination of matter and soul; by what it is distinguished (yat)–by differences among various moving or non-moving bodies; and who (yah) is he (sa)–the knower of the field – the jiva and the paramatma.
The neuter form singular yat and tat are used instead of the masculine, though jiva, paramatma and the field are referred to, by the rule of grammar napumsakam anapumsakennaikavac ca (Panini 1.2.69). If there is a group of items with the same base of various genders including neuter, the neuter gender can be used to indicate all of them. This operation is called eka sesa (single remainder).