SB 4.11.23

avyaktasyāprameyasya
 nānā-śakty-udayasya ca
na vai cikīrṣitaṁ tāta
 ko vedātha sva-sambhavam
Word for word: 
avyaktasya — of the unmanifested; aprameyasya — of the Transcendence; nānā — various; śakti — energies; udayasya — of Him who gives rise to; ca — also; na — never; vai — certainly; cikīrṣitam — the plan; tāta — my dear boy; kaḥ — who; veda — can know; atha — therefore; sva — own; sambhavam — origin.
Translation: 
The Absolute Truth, Transcendence, is never subject to the understanding of imperfect sensory endeavor, nor is He subject to direct experience. He is the master of varieties of energies, like the full material energy, and no one can understand His plans or actions; therefore it should be concluded that although He is the original cause of all causes, no one can know Him by mental speculation.
Purport: 

The question may be raised, “Since there are so many varieties of philosophers theorizing in different ways, which of them is correct?” The answer is that the Absolute Truth, Transcendence, is never subject to direct experience or mental speculation. The mental speculator may be called Dr. Frog. The story is that a frog in a three-foot well wanted to calculate the length and breadth of the Atlantic Ocean on the basis of his knowledge of his own well. But it was an impossible task for Dr. Frog. A person may be a great academician, scholar or professor, but he cannot speculate and expect to understand the Absolute Truth, for his senses are limited. The cause of all causes, the Absolute Truth, can be known from the Absolute Truth Himself, and not by our ascending process to reach Him. When the sun is not visible at night or when it is covered by a cloud in the day, it is not possible to uncover it, either by bodily or mental strength or by scientific instruments, although the sun is there in the sky. No one can say that he has discovered a torchlight so powerful that if one goes on a roof and focuses the torchlight on the night sky, the sun will then be seen. There is no such torchlight, nor is it possible.

The word avyakta, “unmanifested,” in this verse indicates that the Absolute Truth cannot be manifested by any strain of so-called scientific advancement of knowledge. Transcendence is not the subject matter of direct experience. The Absolute Truth may be known in the same way as the sun covered by a cloud or covered by night, for when the sun rises in the morning, in its own way, then everyone can see the sun, everyone can see the world, and everyone can see himself. This understanding of self-realization is called ātma-tattva. Unless, however, one comes to this point of understanding ātma-tattva, one remains in the darkness in which he was born. Under the circumstances, no one can understand the plan of the Supreme Personality of Godhead. The Lord is equipped with varieties of energies, as stated in the Vedic literature (parāsya śaktir vividhaiva śrūyate). He is equipped with the energy of eternal time. Not only does He have the material energy which we see and experience, but He has also many reserve energies that He can manifest in due course of time when necessary. The material scientist can simply study the partial understanding of the varieties of energies; he can take up one of the energies and try to understand it with limited knowledge, but still it is not possible to understand the Absolute Truth in full by dint of material science. No material scientist can foretell what is going to happen in the future. The bhakti-yoga process, however, is completely different from so-called scientific advancement of knowledge. A devotee completely surrenders unto the Supreme, who reveals Himself by His causeless mercy. As stated in Bhagavad-gītā, dadāmi buddhi-yogaṁ tam. The Lord says, “I give him intelligence.” What is that intelligence? Yena mām upayānti te. The Lord gives one the intelligence to cross over the ocean of nescience and come back home, back to Godhead. In conclusion, the cause of all causes, the Absolute Truth, or Supreme Brahman, cannot be understood by philosophical speculation, but He reveals Himself to His devotee because the devotee fully surrenders unto His lotus feet. Bhagavad-gītā is therefore to be accepted as a revealed scripture spoken by the Absolute Truth Himself when He descended to this planet. If any intelligent man wants to know what God is, he should study this transcendental literature under the guidance of a bona fide spiritual master. Then it is very easy to understand Kṛṣṇa as He is.