tatraika-stham jagat krtsnam
pravibhaktam anekadha
apasyad deva-devasya
sarire pandavas tada

"At that time Arjuna could see in the universal form of the Lord the unlimited expansions of the universe situated in one place although divided into many, many thousands."

Sanjaya tells that Arjuna saw many, many things in the Celestial body of the Lord. Pandava = Son of Pandu, Arjuna, apasyad = saw, deva-deva = [in] gods' God [Sri Krishna]'s, sarire = body, krtsnam = without any exception, jagat = entire Universe, anekadha = in many aspects, pravibhakta = thoroughly separated, tat = in that [body], eka-stham = one small fraction. The Lord's very mammoth celestial body [Viswaroopam] is seen by Arjuna. In that body, in one corner, he sees, entire Universe, with all its separate entities, without any exception. Arjuna saw everything in this Universe. Everything was seen thoroughly separated and in all aspects. Deva deva means just like Devas are to us the Lord is to Devas. The Body of the Lord was divine, with divine garlands, garments, ornaments, weapons and other astonishing objects, radiating and with divine fragrance. He sees all the objects of the Universe, thoroughly separated in every aspect. What does this mean? Swami Ramanuja says in his Gita Bhashyam: bhogo, bhogopakarana, bhogastana, bhoktruvargam [भोगो, भोगोपकरण, भोगस्ताना, भोगत्रु वर्गम]. Objects of experience, places for such experience, instruments for experiencing and experiencing people. Thus the objects in this Universe are divided into Four separate categories. We are the experiencing people. We eat, listen, run about, etc., and all these are experiences. So all atman are the people experiencing. We experience various objects. They could be food or music, etc., which are experienced. These are also, like the atman, are many, many. These objects are experienced from various places; like an auditorium for listening to music, or dining hall to eat, etc. To experience, one needs implements, like plate to eat, or eyes or light to read, etc. Thus the Universe is separated in many aspects and Arjuna sees everything. Experiencing persons could be human or animals or trees. Places could be Earth or heaven, etc. All these were seen by Arjuna in the Divine body of the Lord. That too in a small part of the body. The Lord already told that the Lord supported the entire Universe and He said that without Him, there was nothing in the Universe. He had told that He was the Antaryami in everything. He had told that He was the Primary Cause for everything created, sustained and destroyed. Thus in these Five slokas, Sanjaya expalined to Dridarashtra, the scene viewed by Arjuna.