In the beginning of Bhagavad-gita Arjuna was worried about killing Bhisma and Drona, his worshipful grandfathers and masters. But Krsna said that he need not be afraid of killing his grandfather. When they tried to disrobe Draupadi in the assembly, Bhisma and Drona were silent, and for such negligence of duty they should be killed. Krsna 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 Krsna showed him. A devotee is not much interested in the universal form, for it does not enable one to reciprocate loving feelings. A devotee wants to offer his respectful worshiping feelings; thus he wants to see the two-handed or four-handed Krsna form so he can reciprocate in loving service with the Supreme Personality of Godhead.