Sanjay is narrating the scene to the blind king Dhritarashtra back in the palace. He describes what he sees on the battlefield: Arjuna, overwhelmed with compassion, his eyes swimming with tears, sinking under the weight of his own grief. And then — Madhusudana, Krishna, begins to speak.
This is the hinge moment of the Gita. Everything Arjuna said in Chapter 1 — the trembling hands, the dry mouth, the refusal to fight — has led here. He has laid down his bow. He has gone silent. Now it is Krishna's turn.
Sanjay calls Krishna by the name Madhusudana — the one who defeated the demon Madhu. The name is fitting. Just as Krishna once vanquished an external demon, he is about to confront the demon of confusion lodged in Arjuna's mind.