BG Chap 11 - The reason Kṛṣṇa gave Arjuna divine eyes
Since it is not possible to see the universal form with eyes that are used to seeing the form of Kṛṣṇa, Kṛṣṇa gave Arjuna divine eyes, or the eyes of the devas, to behold His majestic form. This form was not caused by magic or illusion. Kṛṣṇa showed Arjuna the heavenly form composed of all the devatās in order to astonish him. The superior eye which sees only the great sweetness of Kṛṣṇa’s human pastimes, like the ananya bhakta, does not at all accept the glories of the Lord’s pastimes in relation to the devatās. One who has tasted the juice of the white lotus cannot relish sugar candy with his tongue. Thus the Lord, wanting to show the majesty of his pastimes with the devatās, in order to cause astonishment in Arjuna who had requested just that, gave to Arjuna non- human eyes suitable for seeing deva līlā. Arjuna could not have seen the form with a thousand heads, shining like a thousand suns at once by his eyes which were accustomed to see only Kṛṣṇa’s sweetness. Although Kṛṣṇa gave Arjuna celestial eyes, He did not give him a celestial mind. If He had given that type of mind to Arjuna, Arjuna would have taken pleasure in that celestial form. Some say that the universal form with a thousand heads is superior to the form of Kṛṣṇa as the chariot driver of Arjuna, and thus Kṛṣṇa had to give Arjuna different eyes to see that universal form. This idea is refuted later.