In the beginning of Bhagavad-gītā Arjuna was worried about killing Bhīṣma and Droṇa, his worshipful grandfather and master. But Kṛṣṇa said that he need not be afraid of killing his grandfather. When the sons of Dhṛtarāṣṭra tried to disrobe Draupadī in the assembly of the Kurus, Bhīṣma and Droṇa were silent, and for such negligence of duty they should be killed. Kṛṣṇa showed His universal form to Arjuna just to show him that these people were already killed for their unlawful action. That scene was shown to Arjuna because devotees are always peaceful and they cannot perform such horrible actions. The purpose of the revelation of the universal form was shown; now Arjuna wanted to see the four-armed form, and Kṛṣṇa showed him. A devotee is not much interested in the universal form, for it does not enable one to reciprocate loving feelings. Either a devotee wants to offer his respectful worshipful feelings, or he wants to see the two-handed Kṛṣṇa form so that he can reciprocate in loving service with the Supreme Personality of Godhead.