In chapter 11 Arjuna asks to see Kṛṣṇa as he truly is, and the request is granted. Sañjaya, who narrates the war, reaches for the only image large enough: if a thousand suns rose at once in the sky, their light might be like the light of that great one.
You would expect the god to speak at this point. He mostly doesn’t.
Count the speakers in chapter 11. Of its 55 verses, Arjuna speaks 33. Kṛṣṇa speaks 14. Sañjaya speaks 8. Across the whole Gītā Kṛṣṇa does nearly all the talking, but in the one chapter where he is seen completely, the balance flips. Arjuna praises, describes, trembles and begs. The infinite stands there and lets him.
Faced with everything, the man talked. Everything listened.
Going deeper
11.12 is Sañjaya's image for the form Arjuna has asked to see: if a thousand suns were to rise at once in the sky, the splendour would be like that of the mighty One. The verse before, 11.11, describes the form wearing divine garlands and garments, anointed with divine perfumes, full of wonders, boundless and facing every direction. 11.13 says Arjuna then saw the whole universe, in all its divisions, gathered in one place within the body of the God of gods. The story watches who talks next. In this chapter the praise, the description and the fear come mostly from Arjuna, with Sañjaya narrating, and Kṛṣṇa speaks little, as the count above shows. The text does not explain why. It lets Arjuna speak. The whole scene is in chapter 11.