There are different kinds of philosophers who have tried to understand the supreme source by their mental speculation. There are generally six kinds of mental speculators, whose speculations are called ṣaḍ-darśana. All these philosophers are impersonalists and are known as Māyāvādīs. Every one of them has tried to establish his own opinion, although they all have later compromised and stated that all opinions lead to the same goal and that every opinion is therefore valid. According to the prayers of the personified Vedas, however, none of them is valid because their process of knowledge is created within the temporary material world. They have all missed the real point: the Supreme Personality of Godhead, or the Absolute Truth, can be understood only by devotional service.
One class of philosophers, known as Mīmāṁsakas, represented by sages such as Jaimini, have concluded that everyone should engage in pious activities or prescribed duties and that such activities will lead one to the highest perfection. But this is contradicted in the Ninth Chapter of the Bhagavad-gītā, where Lord Kṛṣṇa says that by pious activities one may be elevated to the heavenly planets, but that as soon as one’s accumulation of pious activities is used up, one has to leave the enjoyment of a higher standard of material prosperity in the heavenly planets and immediately come down again to these lower planets, where the duration of life is very short and where the standard of material happiness is of a lower grade. The exact words used in the Bhagavad-gītā are kṣīṇe puṇye martya-lokaṁ viśanti (BG 9.21). Therefore the conclusion of the Mīmāṁsaka philosophers that pious activities will lead one to the Absolute Truth is not valid. Although a pure devotee is by nature inclined to perform pious activities, no one can attain the favor of the Supreme Personality of Godhead by pious activities alone. Pious activities may purify one of the contamination caused by ignorance and passion, but this purification is automatically attained by a devotee constantly engaged in hearing the transcendental message of Godhead in the form of the Bhagavad-gītā, Śrīmad-Bhāgavatam or similar scriptures. From the Bhagavad-gītā we understand that even a person who is not up to the standard of pious activities but who is absolutely engaged in devotional service is to be considered well situated on the path of spiritual perfection. It is also said in the Bhagavad-gītā that a person who is engaged in devotional service with love and faith is guided from within by the Supreme Personality of Godhead. The Lord Himself as Paramātmā, or the spiritual master sitting within one’s heart, gives the devotee exact directions by which he can gradually go back to Godhead. The conclusion of the Mīmāṁsaka philosophers is not actually the truth which can lead one to real understanding.
Similarly, there are Sāṅkhya philosophers, metaphysicians or materialistic scientists who study this cosmic manifestation by their invented scientific method and do not recognize the supreme authority of God as the creator of the cosmic manifestation. They wrongly conclude that the reactions of the material elements are the original cause of creation. The Bhagavad-gītā, however, does not accept this theory. It is clearly said therein that behind the cosmic activities is the direction of the Supreme Personality of Godhead. This fact is corroborated by the Vedic injunction sad vā saumyedam agra āsīt, which means that the origin of the creation existed before the cosmic manifestation. Therefore, the material elements cannot be the cause of the material creation. Although the material elements are accepted as immediate causes, the ultimate cause is the Supreme Personality of Godhead Himself. The Bhagavad-gītā says, therefore, that material nature works under the direction of Kṛṣṇa.
The conclusion of the atheistic Sāṅkhya philosophy is that because the effects—the phenomena of this material world—are temporary, or illusory, the cause is therefore also illusory. The Sāṅkhya philosophers are in favor of voidism, but the actual fact is that the original cause is the Supreme Personality of Godhead and that this cosmic manifestation is the temporary manifestation of His material energy. When this temporary manifestation is annihilated, its cause, the eternal existence of the spiritual world, continues as it is, and therefore the spiritual world is called sanātana-dhāma, the eternal abode. The conclusion of the Sāṅkhya philosophers is therefore invalid.