In plain words
This whole world is full of Brahman. The world that is full of Brahman is full of karma. Creation itself is the great karma. The body itself is a great karma. Karma, one can say, is simply a power of the Ātma. It can also be called the power of life. The body is the upādhi of this power of life. To strive, through the body that is the upādhi of the power of life, to recognise one's duty: that is sādhana. The body is the field of karma. The Ātma is the field of Brahman. That is the field of Dharma. So the chief message of this Bhagavad Gītā is to strive to reach Brahman, the field of Dharma, through the body, the field of karma.
Name and form pass; Saccidānanda is eternal and everlasting
In the field called the heart there stands a single wish-fulfilling tree; around it a thicket of trees and thorny scrub has grown. Clear the weeds and look, friends: the wish-fulfilling tree comes into view. That is the wish-granting cow of blessing, that grants every good wish.
It is not enough merely to say in words, “Brahman is real; the world is illusory.” The whole world is full of Brahman! But because this world is made of name and form, it holds both the eternal and the passing. Every single thing has “asti bhāti priyam”: it exists as that very “sat cit ānanda”. For our own use we deal with it by name and form. Only name and form pass away; what is called sat cit ānanda is eternal, everlasting. It is ‘nirguṇaṃ, niraṃjanaṃ, sanātanaṃ, niketanaṃ, nityaśuddha buddhamukta nirmalasvarūpiṇaṃ’. How can such an ever-true principle of the Ātma be called illusory? What is seen has form, but the seeing has none. It is through what is seen that we must experience the seer. So the right sādhana is to experience the seer with a seeing that has no name and form.
To stay in the dealings of the world, keep close ties with them, and give it up: that is very hard.