Below is an essay on the Third chapter of the Bhagvad Gita.
Arjuna is confused about which path to take. With the aid of previous conversations with the Lord, he now knows that the ultimate goal of life is Krishna consciousness but then why should he fight?
Bhagvan then tells about conditioned soul, why they were sent to this material world, what was their prescribed duty, how in time; in influence of the material world he forgot his duty and how he was pushed farther from Krishna consciousness.
Soul is always active and conditioned soul also has the material propensity. So the Lord sent them to this world to enjoy this materiality but in turn they were required to perform yajnas to satisfy the various demi gods. (and in turnVisnu) By being on this path they would gradually control their senses, mind, intelligence and return to the path of self-realization.
However man by his forgetfulness forgot his true aim and worked only for self/sense gratification. He took everything from the Lord but in turn returned nothing. His love for Krisna changed to lust and that was the beginning of his degradation.
An ignorant works for sense gratification, A learned for Krisna. A Krisna conscious person need not perform the prescribed duties (of performing yajnas but still does so, so that others can follow him. It’s known that common people always follow great men.
The ignorant in the beginning while doing the daily work should simultaneously engage themselves in yajnas. Slowly their intelligence makes them detached from material nature and they gradually lead to Krisna consciousness.
Once they are on this path, their love for Krisna is rekindled and slowly they are freed from the results of their past sinful activities.
Thus Krisna says ‘Work as if you are working for ME, surrender tome, chant my name always, be detached and do not worry about results.When you strive on this path; your mind is strengthened, lust does not touch you and then you will be free from the bonds of Karma.
And so Arjuna should fight. As a Kshatriya his job is to fight for dharma, to protect the distressed and because HE says so, he should fight and not bother about the result.