Arjuna addresses Krsna as the grandfather because He is the father of Brahma, the first living creature in the universe. BG 1972 purports
Expressions researched:
"Arjuna also addresses Krsna as the great-grandfather because He is the father of Brahma, the first living creature in the universe"
Bhagavad-gita As It Is
BG Chapters 7 - 12
The Lord is addressed here as air because the air is the most important representation of all the demigods, being all-pervasive. Arjuna also addresses Kṛṣṇa as the great-grandfather because He is the father of Brahmā, the first living creature in the universe.
BG 11.39, Translation and Purport: You are air, and You are the supreme controller! You are fire, You are water, and You are the moon! You are Brahmā, the first living creature, and You are the great-grandfather. I therefore offer my respectful obeisances unto You a thousand times, and again and yet again!
The Lord is addressed here as air because the air is the most important representation of all the demigods, being all-pervasive. Arjuna also addresses Kṛṣṇa as the great-grandfather because He is the father of Brahmā, the first living creature in the universe.