Bhagavad-gita 2.22 Soul changes body like a person changes garments

vasamsi jirnani yatha vihaya navani grhnati naro 'parani
tatha sarirani vihaya jirnany anyani samyati navani dehi ... BG 2.22
As a person puts on new garments, giving up old ones, the soul similarly accepts new material bodies, giving up the old and useless ones.

Change of body by the atomic individual soul is an accepted fact. After old age, the soul is transferred to another body. Transference of the atomic soul to another body is made possible by the grace of the Supersoul.

There are two kinds of souls - namely the minute particle soul (jivatma or anu-atma - limited in quality) and the Supersoul (Paramatma or vibhu-atma - unlimited in quality). This is also confirmed in Katha Upanishad (1.2.20) that states that both the Supersoul and the atomic soul are situated on the same tree of the body within the same heart of the living being. The Supersoul fulfills the desire of the atomic soul as one friend fulfills the desire of another.

In Mundaka Upanisha (3.1.1 & 3.1.2) and Svetasvatara Upanishad (4.6 & 4.7), soul and Supersoul are compared to two friendly birds sitting on the same tree. Of these two birds, one is captivated by the fruits of the material tree while the other is simply witnessing the activities of His friend.

Although they are friends, one is the Master and the other the servant. Forgetfulness of this relationship by the atomic soul is the cause of one's changing his position from one tree to another or from one body to another. This makes the atomic soul struggle very hard engrossed with anxiety and moroseness as the enjoyer of the fruits of the tree or of the material body.

As soon as the atomic soul agrees to accept the other bird as the supreme spiritual master the subordinate bird understand the glories of the Supersoul and becomes free from material desires and lamentations.

Krsna is the fountainhead of the Supersoul and Arjuna is the atomic soul, forgetful of his real nature. Krsna is like the witnessing bird and Arjuna the eating bird. Therefore Arjuna required to be enlightened by Krsna. Since Arjuna had turned his face towards his eternal friend, Krsna, he was understanding the Bhagavad-gita from Him and becoming free from lamentation.