Lord Krishna said: Whatever form of Me (the Supreme) you saw, is extremely rare to see. Even Devas always aspire to see this Universal form!
Krishna emphasizes again that to see the Viśva-rūpa is exquisitely rare, as Arjuna himself has felt. The objectworld cannot have ultimately an object-cause. The source can only be the Subject, which inheres within the object. Is it like a mustard displaying a mountain within? Yes! This indeed is the truth of the object!
The Self is this one Subject, reigning within the body. It produces and preserves the body and all that the senses perceive. This is a mystery, no doubt. Even gods of heavens wish to unravel this. Hence they are anxious to see the Viśva-rūpa, inhering in the Self.
Arjuna should feel encouraged that he has been able to see what even heavenly denizens yearn to. In that way, Viśva-rūpa darshana has been very effective.