(Click to enlarge photo of Srila Prabhupada)
"Unless one hears from a bona fide ācārya, who is never disturbed by the changes of the material world, one cannot have the real key to transcendental knowledge. The bona fide spiritual master, who has also heard the śruti-mantras, or Vedic knowledge, from his undisturbed ācārya, never presents anything that is not mentioned in the Vedic literature. In the Bhagavad-gītā (9.25) it is clearly said that those who worship the pitṛs, or forefathers, attain the planets of the forefathers, that the gross materialists who make plans to remain here stay in this world, and that the devotees of the Lord who worship none but Lord Kṛṣṇa, the supreme cause of all causes, reach Him in His spiritual sky. Here also in Śrī Īśopaniṣad it is verified that one achieves different results by different modes of worship. If we worship the Supreme Lord, we will certainly reach Him in His eternal abode, and if we worship demigods like the sun-god or moon-god, we can reach their respective planets without a doubt. And if we wish to remain on this wretched planet with our planning commissions and our stopgap political adjustments, we can certainly do that also.
Nowhere in authentic scriptures is it said that one will ultimately reach the same goal by doing anything or worshiping anyone. Such foolish theories are offered by self-made 'spiritual masters' who have no connection with the paramparā, the bona fide system of disciplic succession. The bona fide spiritual master cannot say that all paths lead to the same goal and that anyone can attain this goal by his own mode of worship of the demigods or of the Supreme or whatever. Any common man can very easily understand that a person can reach his destination only when he has purchased a ticket for that destination. A person who has purchased a ticket for Calcutta can reach Calcutta, but not Bombay. But the so-called spiritual masters say that any and all paths will take one to the supreme goal. Such mundane and compromising offers attract many foolish creatures, who become puffed up with their manufactured methods of spiritual realization. The Vedic instructions, however, do not uphold them. Unless one has received knowledge from the bona fide spiritual master who is in the recognized line of disciplic succession, one cannot have the real thing as it is."
(Śrī Īśopaniṣad 13, Purport)