God Krishna churned Gita, the sole essence of the nectar in form of Bharata and the vital essence so extracted has been inserted in the mouth (in mind and savvy through ears) of Arjuna by him.
भारतामृतसर्वस्वगीताया मथितस्य च। सारमुद्धृत्य कृष्णेन अर्जुनस्य मुखे हुतम्॥