The Absolute Truth, tattva . . . that is tattva. Vadanti tat tattva-vidaḥ. Who can speak of tattva unless one is completely conversant with the tattva? Tattva means truth. So vadanti tat tattva-vidaḥ. Those who are conversant with the Absolute Truth, they say. What do they say? Vadanti tat tattva-vidas tattvaṁ yaj jñānam advayam (SB 1.2.11). The Absolute Knowledge, without any duality, advayam. What is that? Now, Brahman, Paramātmā and Bhagavān.
The Absolute Truth is described in different ways by different people according to angle of vision. But the object is the same. There may be different types of religious systems, but the object is Kṛṣṇa. Somewhere it is openly expressed, and somewhere it is covered. Just like Brahman, Brahman realization, impersonal realization, Brahman realization. For the jñānīs, those who are seeking out the Absolute Truth by speculative knowledge, they want to make these varieties of material world as void, the Buddha philosophy, śūnyavādi. Because they are disgusted with these material varieties, therefore they want something opposite. That opposite is voidism, śūnyavāda. The śūnyavāda or, little more further, that is brahmavāda, without any varieties, simply the light, brahma-jyotir. This is also another realization. Śūnyavāda, to make this material world null and void, they come to the impersonal Brahman effulgence. This is Brahman realization.
And then, for the yogīs, the localized aspect, Paramātmā. Īśvaraḥ sarva-bhūtānāṁ hṛd-deśe 'rjuna tiṣṭhati (BG 18.61). By meditation. This is Paramātmā realization. And then, ultimately, Bhagavān, the Supreme Personality of Godhead. Just like we general, people in general, we can see the sunshine, but everyone knows—at least, scientists know—that the sunshine is coming from the sun globe. If you have got power to go to the sun globe, you can see what actually the sun globe is. And if you go still further, penetrate into the sun globe, then you will see there is a sun-god, sun-god. His name is also described in the Bhagavad-gītā: Vivasvān. In the beginning of this chapter, Fourth Chapter, Kṛṣṇa said, imaṁ vivasvate yogaṁ proktavān aham avyayam (BG 4.1). So within the sun globe there is the person, the predominating deity whose name is Vivasvān.