sanjaya uvaca
ity arjunam vasudevas tathoktva
svakam rupam darsayam asa bhuyah
asvasayam asa ca bhitam enam
bhutva punah saumya-vapur mahatma

"Sanjaya said to Dhritarashtra: The Supreme Personality of Godhead, Krishna, having spoken thus to Arjuna, displayed His real four-armed form and at last showed His two-armed form, thus encouraging the fearful Arjuna."

Sanjaya tells that the Lord conceding to the prayer of Arjuna, reverts back to the more pleasant form with Four arms, carrying discus and conch, and as the normal chariot driver of Arjuna, and assuaged Arjuna. In the earlier sloka, the Lord assured that He would get back to His usual Form and in this sloka He actually gets back to the usual form to assuage Arjuna. Sanjaya narrates that the Lord had reverted back to the usual Form. Ity Arjunam = thus Arjuna, tathoktva = was told by, vasudeva = Sri Krishna, svakam = [Sri Krishna's] Self, rupam = image, bhuya = again, dharsayamasa = made visible [to Arjuna]. That is the Lord made Himself in His usual form, viewable by Arjuna. Asvasayam asa = assuaged [Arjuna], bhitam enam = wiped off his fears. How? Puna = [by] again, sowmya-vapu = beautiful or pleasant appearance. By taking the usual pleasant form, the Lord assuaged Arjuna. Here, we may have doubt. Is it possible to change the appearance? After all a person is what he is. Beauty of atman is in knowledge, devotion and good qualities. If these are proper, body beauty is immaterial. Also, even if we struggle hard, changing the body's form is very difficult. When this is the case, how the Lord suddenly changed the gigantic form to the usual pleasant form? The answer is in the word mahatma = great soul [ of Sri Krishna]. The Lord has the capacity to do what He decided [satya sankalpam]. Mahatma implies this quality of satya sankalpa. It is no wonder, as the Lord did this as a just born infant! In the sloka it is said that the Lord appeared in His usual pleasant appearance. Our ancestors and commentators interpret that the Lord appeared with Four arms, carrying discus and conch in the upper arms. But Sri Krishna had only Two arms. So how Four arms are mentioned? In the prison of Kamsa in Mathura, the Lord was born as an infant with Four arms and with all ornaments. All puranas like Srimad Bhagavatam, describe that the Lord appeared with all the Divine weapons and ornaments. Seeing this, father Vasudeva [वसुदेव] requested the Lord to hide the divine appearance with Four arms and appear like any normal child. The Lord did accordingly. Thus Four arms are natural for the Lord. To avoid detection by Kamsa, the Lord was with Two arms till the age of 10 in Gokulam. Puranas say that लेटर, He was with Four arms. Therefore, Four arms is His usual Self.