Explanation:

God always selects a liberated soul with a gross body for becoming the human incarnation. God will not enter a human gross body directly without the liberated soul. If that were done, the liberated soul would lose the chance of enjoying the closest association with God in a single body. Also the liberated soul would not get the credit of being treated as God (Advaita). Especially when God preaches the exceptional spiritual knowledge like the Gita, the liberated soul is treated as the generator of such exceptional knowledge. Apart from this, God also has an advantage in the association with the liberated soul. God cannot act as a really ignorant person, since ignorance can never cover Him completely. Even the thickest cloud cannot retain its original intensity of darkness when it tries to cover the bright sun. Similarly, when ignorance covers God, it cannot retain its original state of ignorance and becomes weak[1]. Hence, God likes the association of a liberated soul, which can attain the inherent ignorance of a soul in doing ignorant activities. It is like a dupe acting on behalf of the hero in disguise of the hero during a cinema shooting. Instead of God acting like an ignorant soul, it will be better if a really ignorant soul acts on behalf of God in disguise. Even though the liberated soul is enlightened and is devoid of ignorance, it can attain its inherent state of ignorance in a natural way whenever it is required. It is easier for an illuminated cloud to regain its darkness than it is for the inherently bright sun to become dark by covering itself with a cloud. Due to the close association with the ignorant soul, God appears to be really ignorant through the soul and thus God can test the real faith of devotees. God takes the credit of the ignorant actions of the associated liberated soul and in turn the liberated soul takes the credit of God’s wonderful activities. Thus, the purpose of God as well as the ambition of the soul is accomplished by this mutual exchange. This is the main reason of the association of God with the selected liberated soul in the human incarnation as per the Veda (Dvaa suparnaa…). The ambition of God to taste real ignorance and the ambition of the soul to taste real divinity are simultaneously accomplished.

[1] The ignorance is reduced. Partial knowledge appears.