CC Ādi 17.275
catur-vidha bhakta-bhāva kare āsvādana
The same Supreme Personality of Godhead who appeared as the son of mother Yaśodā has now appeared as the son of mother Śacī, relishing four kinds of devotional activities.
Servitude, friendship, parental affection and conjugal love for the Supreme Personality of Godhead are the basis of the four kinds of devotional activities. In śānta, the marginal stage of devotional service, there is no activity. But above the śānta humor are servitude, friendship, parental affection and conjugal love, which represent the gradual growth of devotional service to higher and higher platforms.