SB 5.12.12

rahūgaṇaitat tapasā na yāti
 na cejyayā nirvapaṇād gṛhād vā
na cchandasā naiva jalāgni-sūryair
 vinā mahat-pāda-rajo-’bhiṣekam
Word for word: 
rahūgaṇa — O King Rahūgaṇa; etat — this knowledge; tapasā — by severe austerities and penances; na yāti — does not become revealed; na — not; ca — also; ijyayā — by a great arrangement for worshiping the Deity; nirvapaṇāt — or from finishing all material duties and accepting sannyāsa; gṛhāt — from ideal householder life; vā — or; na — nor; chandasā — by observing celibacy or studying Vedic literature; na eva — nor; jala-agni-sūryaiḥ — by severe austerities such as keeping oneself in water, in a burning fire or in the scorching sun; vinā — without; mahat — of the great devotees; pāda-rajaḥ — the dust of the lotus feet; abhiṣekam — smearing all over the body.
Translation: 
My dear King Rahūgaṇa, unless one has the opportunity to smear his entire body with the dust of the lotus feet of great devotees, one cannot realize the Absolute Truth. One cannot realize the Absolute Truth simply by observing celibacy [brahmacarya], strictly following the rules and regulations of householder life, leaving home as a vānaprastha, accepting sannyāsa, or undergoing severe penances in winter by keeping oneself submerged in water or surrounding oneself in summer by fire and the scorching heat of the sun. There are many other processes to understand the Absolute Truth, but the Absolute Truth is only revealed to one who has attained the mercy of a great devotee.
Purport: 

Actual knowledge of transcendental bliss can be bestowed upon anyone by a pure devotee. Vedeṣu durlabham adurlabham ātma-bhaktau. One cannot attain the perfection of spiritual life simply by following the directions of the Vedas. One has to approach a pure devotee: anyābhilāṣitā-śūnyaṁ jñāna-karmādy-anāvṛtam. By the grace of such a devotee, one can understand the Absolute Truth, Kṛṣṇa, and one’s relationship with Him. A materialistic person sometimes thinks that simply by executing pious activities and remaining at home one can understand the Absolute Truth. That is denied in this verse. Nor can one understand the Absolute Truth simply by observing the rules and regulations of brahmacarya (celibacy). One only has to serve the pure devotee. That will help one understand the Absolute Truth without fail.