Ātma-tattva is the science of both God and the living entity. Both the Supreme Lord and the living entity are known as ātmā. The Supreme Lord is called Paramātmā, and the living entity is called the ātmā, the brahma or the jīva. Both the Paramātmā and the jīvātmā, being transcendental to the material energy, are called ātmā. So Śukadeva Gosvāmī explains this verse with the aim of purifying the truth of both the Paramātmā and the jīvātmā. Generally people have many wrong conceptions about both of them. The wrong conception of the jīvātmā is to identify the material body with the pure soul, and the wrong conception of Paramātmā is to think Him on an equal level with the living entity. But both misconceptions can be removed by one stroke of bhakti-yoga, just as in the sunlight both the sun and the world and everything within the sunlight are properly seen. In the darkness one cannot see the sun, nor himself, nor the world. But in the sunlight one can see the sun, himself and the world around him. Śrīla Śukadeva Gosvāmī therefore says that for purification of both wrong conceptions, the Lord presented His eternal form before Brahmājī, being fully satisfied by Brahmā's nondeceptive vow of discharging bhakti-yoga. Except for bhakti-yoga, any method for realization of ātma-tattva, or the science of ātmā, will prove deceptive in the long run.
In the Bhagavad-gītā, the Lord says that only by bhakti-yoga can one know Him perfectly, and then one can enter into the science of God. Brahmājī undertook great penance in performing bhakti-yoga, and thus he was able to see the transcendental form of the Lord. His transcendental form is one hundred percent spiritual, and one can see Him only by spiritualized vision after proper discharge of tapasya or penance, in pure bhakti-yoga. The form of the Lord manifested before Brahmā is not one of the forms with which we have experience in the material world. Brahmājī did not perform such severe types of penance just to see a form of material production. Therefore the question by Mahārāja Parīkṣit about the form of the Lord is answered. The form of the Lord is sac-cid-ānanda (BS 5.1), or eternal, full of knowledge and full of bliss. But the material form of the living being is neither eternal, nor full of knowledge, nor blissful. That is the distinction between the form of the Lord and that of the conditioned soul. The conditioned soul, however, can regain his form of eternal knowledge and bliss simply by seeing the Lord by means of bhakti-yoga.