What is the essence of Shrimad Bhagwat Geeta?

1) Only the one, who has become Krishna Himself, can say what Lord Krishna was trying to say in the two words. No one else can. Today, 'we' have come as Krishna so whatever work you need to get done, get it done. What did Lord Krishna mean? When a person dies, what is it that leaves when people say, "He left the body?" That, which leaves, is the 'real thing' and whatever is left behind is the 'packing'. What you see with your physical eyes is the packing and the material (Soul or Atma) is within. There are varieties of packings. Some are in the form of a tree, some in the form of a donkey, some in the form of a man or a woman, etc., but the material, the content within each is the same. The packing can be in any form; it can even be rotten but a businessman is not really concerned with the outer packing, he is only concerned with the material within. Similarly, you should do the darshan of that material (the Self, the Lord) within the packing (body).

2) What the Lord said was, "When you go to buy vegetables, expect to get vegetables, however, having bought them, if they turn out bitter, then that is your reward. Therefore, do not have expectations for the rewards and do not do raag-dwesh. Accept whatever happens in the end." Maintain composure if your pocket gets picked. Do not lament over it. Maintain equanimity there. If you go out to buy a sari, naturally you expect to get a sari, but do not get depressed if it turns out to be a bad one. Accept the sari as it is. Do not expect anything more than that. Do not do raag-dwesh; that is what Lord Krishna is trying to say. You can go to a shoe store but do not harbor feelings of right or wrong, likes and dislikes. Therefore, nishkam karma is to not harbor like or dislike in the result of any effort.