एवमुक्त्वा ततो राजन्महायोगेश्वरो हरिः। दर्शयामास पार्थाय परमं रूपमैश्वरम् ॥

evam uktvā tato rājan mahā-yogeśhvaro hariḥ darśhayām āsa pārthāya paramaṁ rūpam aiśhwaram

Having thus spoken, O King, the great Lord of Yoga, Hari, showed to Pârtha His supreme Form as Lord.

In plain words: Sanjaya, the narrator telling the story to the blind King Dhritarashtra, says that Krishna (also called Hari), the great master of yoga, now showed Arjuna (Partha) His highest form as Lord of all.