Visvarupa Darsana Yoga-Bhagavad Gita Chapter 11 [The Vision of the Universal Form]
Krishna Said > Shaloka: 49
Your mind has been perturbed upon seeing this horrible feature of Mine. Now let it be finished. My devotee, be free from all disturbance. With a peaceful mind you can now see the form you desire.
In the beginning of Bhagavad-gita Arjuna was worried about killing Bhisma and Drona, his worshipful grandfathers and masters. But Krishna 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. Krishna 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 Krishna 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 Krishna form so he can reciprocate in loving service with the Supreme Personality of Godhead.