CC Madhya 22.17

kṛṣṇa-bhakti haya abhidheya-pradhāna
bhakti-mukha-nirīkṣaka karma-yoga-jñāna
Synonyms: 
kṛṣṇa-bhakti — devotional service to Lord Kṛṣṇa; haya — is; abhidheya-pradhāna — the chief function of the living entity; bhakti-mukha — of the face of devotional service; nirīkṣaka — observers; karma-yoga-jñāna — fruitive activities, mystic yoga and speculative knowledge.
Translation: 
“Devotional service to Kṛṣṇa is the chief function of the living entity. There are different methods for the liberation of the conditioned soul — karma, jñāna, yoga and bhakti — but all the others are dependent on bhakti.