CC Madhya 24.171

ca-śabda api-arthe, ‘api’ — avadhāraṇe
yatnāgraha vinā bhakti nā janmāya preme
Synonyms: 
ca-śabda — the word ca; api — of the word api; arthe — in the sense; api avadhāraṇe — this api is used for emphasis; yatna-āgraha vinā — without sincere endeavor; bhakti — devotional service; — not; janmāya — begets; preme — love of Godhead.
Translation: 
“The word ‘ca’ may be used in place of ‘api,’ which gives emphasis to something. Thus it means that without sincere endeavor in devotional service, one cannot attain love of Godhead.