सर्वोपनिषदो गावो दोग्धा गोपालनंदनः । पार्थो वत्सः सुधीर्भोक्तादुग्धं गीतामृतः महत् ॥. This Gitopanisad, Bhagavad-gita, the essence of all the Upanishads, is just like a cow, and Lord Krishna, who is famous as a cowherd boy, is milking this cow.  Arjuna is just like a calf and learned scholars and pure devotees are to drink the nectarean milk of Bhagavad-gita [Gita mahatmya 6]