Sanjaya uvaacha:
evamuktvaa tato raajanmahaayogeshvaro harihi |
darshayaamaasa paarthaaya paramam roopamaishvaram || 9 ||

Sanjaya said:
O King, then having spoken this, Hari, the great Yogeshwara, showed the supreme form of Ishvara to Paartha.

evam : this
uktvaa : having spoken
tataha : then
raajan : O King
mahaayogeshvaraha : great Yogeshwara
harihi : Hari
darshayaamaasa : showed
paarthaaya : to Paartha
paramam : supreme
roopam : form
aishvaram : of Ishvara
At this point in the Gita, neither Shri Krishna nor Arjuna could continue narrating since Shri Krishna was showing the cosmic form, and Arjuna was taking it all in. The great sage Veda Vyaasa, the compiler of the Mahaabhaarata, chose to switch the narration over to Sanjaya, who was relaying the events to Dhritraashtra, the “King” that is mentioned in this shloka.
We notice a subtle shift in the language used by Sanjaya. His praise of Shri Krishna is one degree higher than that used by Arjuna. For instance, he refers to Shri Krishna as “Mahaa Yogeshwara” whereas Arjuna uses “Yogeshwara”. It is because Sanjaya knew Shri Krishna more thoroughly and deeply than Arjuna did. Moreover, he was already blessed with divine vision through Vyaasa, which enabled him to see exactly what Arjuna saw.
Sant Jnyaneshwara’s commentary of this shloka emphasizes Arjuna’s good fortune of being able to view this cosmic form. He lists Lakshmi, Shesha and Garuda as tireless servants of Lord Vishnu who have yet to see the cosmic form that Arjuna sees, underscoring the love Shri Krishna for his devotee Arjuna. He also enumerates others who were able to see a tiny glimpse of this cosmic form including Yashoda and Dhruva.
So what did this form look like? The description begins in the next shloka.