The purpose of Śrīmad Bhāgavatam is to glorify the Supreme Absolute Truth, known as Śrī Kṛṣṇa, for the benefit of the suffering humanity. Śrī Vyāsa himself calls this Purāṇa the ripened fruit of the Vedic tree and compares it to the personification of rasa, or devotional relish. It is to be tasted by the rasikas, the connoisseurs of rasa, and relished by the sahṛdayas, the sober-hearted people or those whose hearts are imbued with sattva (SB 1.1.3)
Veda is also a living being. Veda is also a person, not just a book. When somebody studies Vedas without studying Puranas, Veda becomes scared because people will misinterpret. Itihasa and Purana help Veda by establishing her meaning. It is the Puranas which are the authoritative source for knowing the absolute.
