SB 2.6.38
yasyavatara-karmani
gayanti hy asmad-adayah
na yam vidanti tattvena
tasmai bhagavate namah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Let us offer our respectful obeisances unto that Supreme Personality of Godhead, whose incarnations and activities are chanted by us for glorification, though He can hardly be fully known as He is.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
It is said that the transcendental name, form, quality, pastimes, paraphernalia, personality, etc., cannot possibly be perceived by the gross materialistic senses. But when the senses are purified by the process of hearing, chanting, remembering, and worshiping the lotus feet of the holy Deity, etc., the Lord reveals Himself proportionately to the advancement of the quality of devotional service (ye yatha mam prapadyante). One should not expect the Lord to be an order-supplying agent who must be present before us as soon as we desire to see Him. We must be ready to undergo the prescribed devotional duties, following the path shown by the predecessors in the disciplic succession from Brahma, Narada and similar authorities. As the senses are progressively purified by bona fide devotional service, the Lord reveals His identity according to the spiritual advancement of the devotee. But one who is not in the line of devotional service can hardly perceive Him simply by calculations and philosophical speculations. Such a hard worker can present a jugglery of words before an audience, but can never know the Supreme Personality of Godhead in His personal feature. The Lord has clearly stated in the Bhagavad-gita that one can know Him only by devotional service. No one can know the Lord by any puffed-up material process of challenge, but the humble devotee can please the Lord by his earnest devotional activities. Thus the Lord reveals Himself proportionately before the devotee. Lord Brahma therefore offers his respectful obeisances as a bona fide spiritual master and advises us to follow the process of sravana and kirtana. Simply by this process, or simply by hearing and chanting the glories of the activities of the Lord’s incarnation, one can certainly see within himself the identity of the Lord. We have already discussed this subject in volume one of Srimad-Bhagavatam, in connection with this verse:
tac chraddadhana munayo
jñana-vairagya-yuktaya
pasyanty atmani catmanam
bhaktya sruta-grhitaya
(Bhag. 1.2.12)
The conclusion is that one cannot know the Supreme Personality of Godhead fully by any method, but He can be seen and felt partially by the devotional service process of hearing, chanting, etc.