Chapter 2 could be understood as a high level summary of the entire Geetha. It touches on the most salient features of each of the subsequent chapters.
From chapter 3 until chapter 6, bhagavan basically explains how a student needs to prepare himself in order to fully grasp /understand and appreciate the knowledge that is going to be imparted to him in chapters 7-12.
Through the explanations about what karma yoga, jnana yoga,yoga of renunciation and yoga of meditation, Bhagavan wants the student to under go transformation to his mindset, attitude and approach to life , his understanding about himself and all those around him . That sacrificing his every action be it a physical , mental , involuntary, voluntary , to the almighty will free him from the sense of " I am doing this or that" , there by freeing him from the bondage of ownership of such actions . By so doing he is free from desires, anger, greed and so on.
Bhagavan explains how this calming down of the mind by totally with drawing from one's senses can bring about this transformation, and only then the student will be ready to fully comprehend the knowledge that is imparted to him. The student needs to practice this , with steadfastness and complete faith ,because to reach that state of mind requires a lot of effort.
He explains why the knowledge he is going to impart is important and how and why that is going to help the student integrate with the supreme.
In the last sloka of chapter 6 Bhagavan gives a very precise definition of a person who is truly ready to move on to acquire this supreme knowledge .The nature of the Lord, as well as the devotee who is of this kind and his mode of worship, all these he expounds in the Chapters 7 -12.