Because the description of the moon planet does not tally. We have got in the Śrīmad-Bhāgavatam . . . the, this moon planet is one of the heavenly planets. There, very high class of demigods, they live. Or one who is elevated to the moon planet, he is living there for ten thousands of years. Ten . . . what kind of ten thousands of years? In the moon planet, one day equal to our six months. Such months' year, and ten thousands of years. That is the duration of life in the moon planet. Those who are karma-kāṇḍīya, perform ritualistic ceremonies very nicely, they are promoted to the moon planet. And there are other planets also. This, Svargaloka. There are seven planetary system upwards, and seven planetary system downwards. Now we are living in the Bhūrloka, middle. Then above this, there is Bhuvarloka. Above this, there is Svarloka. Above this is Janaloka, Maharloka, Tapoloka, Brahmaloka. So this āroha . . . you cannot go to the Brahmaloka, although there is śāstra . . . or you cannot go to the sun planet also. You are seeing every day, but go there . . . but you have no right. You cannot go.
So therefore this process that, "I shall go by my strength. I shall know by dint of my own knowledge, research work," these are all rascaldom. It is not possible. So what to speak of understanding God? You cannot understand even what is in your presence, the material world, and spiritual is beyond the sky. Paras tasmāt tu bhāvaḥ anyaḥ (BG 8.20). That is another sky. You have no estimation of this sky. Not only this, this sky; even in the material world, this is one universe. What sky we see, that is of one universe. But there are innumerable universes. That is material world. And beyond that, there is spiritual sky. Then the spiritual world begins. There are also planets, Vaikuṇṭha planets. And above these Vaikuṇṭha planets, there is Kṛṣṇaloka. That is Kṛṣṇa's abode. Cintāmaṇi-prakara-sadmasu kalpa-vṛkṣa-lakṣāvṛteṣu (Bs. 5.29).