sanātana grantha kailā 'bhāgavatāmṛte'
bhakta-bhakti-kṛṣṇa-tattva jāni yāhā haite
sanātana—Sanātana Gosvāmī; grantha—books; kailā—compiled; bhāgavata-amṛte—in the Bhāgavatāmṛta; bhakta—devotee; bhakti—devotional service; kṛṣṇa-tattva—Kṛṣṇa, the Absolute Truth; jāni—we know; yāhā haite—from which.
Śrīla Sanātana Gosvāmī compiled the Bhāgavatāmṛta. From this book one can understand who is a devotee, what is the process of devotional service, and who is Kṛṣṇa, the Absolute Truth.
Link to this page: https://prabhupadabooks.com/cc/antya/4/219