Yagna - the fire worship was the central ritual of Indian Ancient Civilization which continued till now. Krishna now explains his descend in Man and animal plane . This is the plane where the soul is visible to highest extent. Yagna is seen as a central cause of outer visibility.
On man ,krishna is the king, and here he refers that the king is one of the highest expression of soul . In the whole Bhagvad Gita , Lord Krishna emphasizes the concept of YAgna or sacrifice by which the world is maintained .