Kṛṣṇa said, "I will not fight." But when Arjuna was practically devastated by the arrows of Bhīṣma, he fell down, his chariot broke, everything shattered. Now Kṛṣṇa saw, "Now Arjuna is going to die." So immediately Kṛṣṇa took the wheel of the chariot and went to the front of Bhīṣma: "Now you stop; otherwise I will kill you." So this is fighting.
Kṛṣṇa asked Arjuna that "You declare to the world that My devotees will never be vanquished." Why Kṛṣṇa asking Arjuna to declare? He could declare. He could declare, but the meaning is that sometimes, for the sake of His devotee, He breaks His promise. For the sake of His devotee. Just like Bhīṣma. Bhīṣma promised, "Kṛṣṇa, tomorrow either Your friend Arjuna will die, I am determined now, or You have to break Your promise." Because Kṛṣṇa said, "I will not fight." But when Arjuna was practically devastated by the arrows of Bhīṣma, he fell down, his chariot broke, everything shattered. Now Kṛṣṇa saw, "Now Arjuna is going to die." So immediately Kṛṣṇa took the wheel of the chariot and went to the front of Bhīṣma: "Now you stop; otherwise I will kill you." So this is fighting. So Bhīṣma saw, "Now Kṛṣṇa has broken His promise. I stop." So to keep the promise of Bhīṣma, that Bhīṣma promised, "Either Arjuna will die, or Kṛṣṇa, You will have to break Your promise," two things, so Kṛṣṇa said, "Yes, I am breaking My promise. Don't kill Arjuna." Therefore, for the sake of devotee, He sometimes break His promise.