The study of Bhagavad Gita is for bhagvad darshan. The darshan that we get of the Lord is the essence of Bhagavad Gita.
If one renders even a small amount of sincere devotional service, Krishna becomes obliged to elevate such a person and what to speak of one whose entire life and soul has been dedicated to Krishna's service.
When we become advanced, we recognize the service of other devotees and we develop our appreciation for them and it manifests in the form of friendship.
Love of God is the real source of happiness and when one abandons that loving real relationship of God, he suffers.