SB 3.32.37

prāvocaṁ bhakti-yogasya
 svarūpaṁ te catur-vidham
kālasya cāvyakta-gater
 yo ’ntardhāvati jantuṣu
Synonyms: 
prāvocam — explained; bhakti-yogasya — of devotional service; svarūpam — the identity; te — to you; catuḥ-vidham — in four divisions; kālasya — of time; ca — also; avyakta-gateḥ — the movement of which is imperceptible; yaḥ — which; antardhāvati — chases; jantuṣu — the living entities.
Translation: 
My dear mother, I have explained to you the process of devotional service and its identity in four different social divisions. I have explained to you as well how eternal time is chasing the living entities, although it is imperceptible to them.
Purport: 

The process of bhakti-yoga, devotional service, is the main river flowing down towards the sea of the Absolute Truth, and all other processes mentioned are just like tributaries. Lord Kapila is summarizing the importance of the process of devotional service. Bhakti-yoga, as described before, is divided into four divisions — three in the material modes of nature and one in transcendence, which is untinged by the modes of material nature. Devotional service mixed with the modes of material nature is a means for material existence, whereas devotional service without desires for fruitive result and without attempts for empirical philosophical research is pure, transcendental devotional service.