On every side, all-swallowing, fiery-tongued, Thou lickest up mankind, devouring all; The glory filleth space: the universe Is burning, Vishnu, with Thy blazing rays.
In plain words: Arjuna sees God's form swallowing people on every side with fiery tongues. Its blazing light fills space, and the whole universe seems to burn. Vishnu is a name for God.