The Puranas are not neutral. Each promotes a deity, and the collection as a whole is best read as the literature of competing devotional movements consolidating in the same idiom. The conventional sorting puts six under Vishnu, six under Shiva and six under Brahma, and the Padma Purana supplies a sharper version: it classifies the eighteen by the three gunas, assigning the Vaishnava texts to sattva, purity, the Shaiva to tamas, darkness, and the rest to rajas. This is presented as description; it is a Vaishnava polemic, and the Shaiva Puranas return the compliment. The Markandeya Purana contains, in the section called the Devi Mahatmya, the foundational scripture of goddess worship, recited entire in Shakta ritual and at Durga Puja.
The Bhagavata Purana is the most consequential of them. Twelve skandhas, some 18,000 verses, and a tenth book on the childhood and youth of Krishna, the butter theft, the lifting of Govardhana, the flute, the circle dance with the cowherd women, that supplied Indian devotional poetry, painting, dance and drama with their central repertoire for a thousand years. It is also self-consciously literary, imitating Vedic language, and philosophically ambitious, arguing that devotion rather than knowledge or ritual is the highest path.
Scholars generally place its composition in the ninth or tenth century CE and argue on linguistic grounds and on its evident debt to the Tamil Alvar poets for an origin in southern India; al-Biruni lists it around 1030, which fixes an upper limit. Tradition assigns it to Vyasa as his final and completing work.
Its influence runs through the entire later devotional map: Chaitanya in Bengal, Vallabha in the west, and the vernacular retellings, Potana's Telugu version, Eknath's Marathi, the Bhagavata Mela dance-drama, which carried it to audiences who read no Sanskrit at all.