Chapter 1 focuses on Arjuna's condition of utter despair. It describes the perfect mental attitude in which to sow the Gita seeds.
In chapter 2, we get an exhaustive summary of the whole philosophical content of the Gita. We are introduced to Sankhya yoga, the logic of reasoning by which the true nature of the Absolute Reality is comprehended. Actions performed without ego, egocentric desires and anxiety for its fruits, with an attitude of offering to the Lord, becomes karma yoga.
Chapter 3 reveals this philosophy and prepares us to face life's battle-fields.
In chapter 4, Krishna dons his divine apparel reinterpreting the ancient sacred Vedic science. He endorses the greater path of jnana yoga, through which all pilgrims must pass to reach the temple of the Self.