rūpa-gosāñi kailā 'rasāmṛta-sindhu' sāra
kṛṣṇa-bhakti-rasera yāhāṅ pāiye vistāra
rūpa-gosāñi—Śrīla Rūpa Gosvāmī; kailā—compiled; rasāmṛta-sindhu—the book known as Bhakti-rasāmṛta-sindhu; sāra—the essence of knowledge in devotional service; kṛṣṇa-bhakti-rasera—of the transcendental mellow in devotional service; yāhāṅ—wherein; pāiye—we can get; vistāra—elaboration.
Śrīla Rūpa Gosvāmī also wrote many books, the most famous of which is Bhakti-rasāmṛta-sindhu. From that book one can understand the essence of devotional service to Kṛṣṇa and the transcendental mellow one can derive from such service.
Link to this page: https://prabhupadabooks.com/cc/antya/4/223