CC Madhya 24.313

ahaṁ vedmi śuko vetti
vyāso vetti na vetti vā
bhaktyā bhāgavataṁ grāhyaṁ
na buddhyā na ca ṭīkayā
Synonyms: 
aham — I (Lord Śiva); vedmi — know; śukaḥ — Śukadeva Gosvāmī; vetti — knows; vyāsaḥ — Vyāsadeva; vetti — knows; na vetti — or may not know; bhaktyā — by devotional service (executed in nine different processes); bhāgavatam — the Bhāgavata Purāṇa (called the Paramahaṁsa-saṁhitā, the text or treatise readable by the topmost transcendentalists); grāhyam — to be accepted; na — not; buddhyā — by so-called intelligence or experimental knowledge; na — nor; ca — also; ṭīkayā — by imaginary commentary.
Translation: 
“[Lord Śiva said:] ‘I may know; Śukadeva Gosvāmī, the son of Vyāsadeva, may know; and Vyāsadeva may know or may not know Śrīmad-Bhāgavatam. On the whole, Śrīmad-Bhāgavatam, the spotless Purāṇa, can be learned only through devotional service, not by material intelligence, speculative methods or imaginary commentaries.’ ”
Purport: 

Devotional service includes nine processes, beginning with hearing, chanting and remembering the activities of Lord Viṣṇu. Only one who has taken to devotional service can understand Śrīmad-Bhāgavatam, which is the spotless Purāṇa for a transcendentalist (paramahaṁsa). So-called commentaries are useless for this purpose. According to the Vedic injunction, yasya deve parā bhaktir yathā deve tathā gurau. All Vedic literatures maintain that Śrīmad-Bhāgavatam has to be learned from the person bhāgavata, and to understand it one has to engage in pure devotional service. Śrīmad-Bhāgavatam cannot be understood by so-called erudite scholars or grammarians. One who has developed pure Kṛṣṇa consciousness and has served the pure devotee, the spiritual master, can understand Śrīmad-Bhāgavatam. Others cannot.