CC Madhya 22.19
na śobhate jñānam alaṁ nirañjanam
kutaḥ punaḥ śaśvad abhadram īśvare
na cārpitaṁ karma yad apy akāraṇam
This is a quotation from Śrīmad-Bhāgavatam (1.5.12). Even after writing many Vedic literatures, Vyāsadeva felt very morose. Therefore his spiritual master, Nāradadeva, told him that he could be happy by writing about the activities of the Supreme Personality of Godhead. Up to that time, Śrīla Vyāsadeva had written the karma-kāṇḍa and jñāna-kāṇḍa sections of the Vedas, but he had not written about upāsanā-kāṇḍa, or bhakti. Thus his spiritual master, Nārada, chastised him and advised him to write about the activities of the Supreme Personality of Godhead. Therefore Vyāsadeva began writing Śrīmad-Bhāgavatam.