Arjuna wanted to see the universal form of the Supreme Lord, so out of His mercy upon His devotee Arjuna, Lord Krishna showed His universal form full of effulgence and opulence. This form was glaring like the sun, and its many faces were rapidly changing. Krishna showed this form just to satisfy the desire of His friend Arjuna. This form was manifested by Krishna through His internal potency, which is inconceivable by human speculation. No one had seen this universal form of the Lord before Arjuna, but because the form was shown to Arjuna, other devotees in the heavenly planets and in other planets in outer space could also see it. They did not seen it before, but because of Arjuna they were able to see it. In other words, all the disciplic devotees of the Lord could see the universal form which was shown to Arjuna by the mercy of Krishna. Someone commented that this form was shown to Duryodhana also when Krishna went to Duryodhana to negotiate for peace. Unfortunately, Duryodhana did not accept the peace offer, but at that time Krishna manifested some of His universal forms. But those forms are different from this one shown to Arjuna. It is clearly said that no one has ever seen this form before.