Purport

Sanjaya who was dictating the whole conversation between Arjuna and Bhagavan Shri Krishna to Dhritarashtra then tells, after giving the introduction about his real universal form and giving Arjuna the cosmic vision, Bhagavan Shri Krishna then reveals his original form to Arjuna. This form is known as the Vishva Rupa or the Universal Form of Shri Krishna.

This is is to remind you that Sanjaya was already granted a cosmic vision by Sage Ved Vyasa. Initially, Shri Ved Vyasa wanted to grant cosmic vision to Dhritarashtra, so he can witness the war. But he refused to say he did not see his children grow and so he doesn't want to see them dying. He requested Shri Ved Vyasa to grant that vision to Sanjaya so he can dictate things as happening in Kurukshetra. This is the above dictation by Sanjaya.