CC Ādi 3.112

ei ślokera artha kahi saṅkṣepera sāra
bhaktera icchāya kṛṣṇera sarva avatāra
Synonyms: 
ei — this; ślokera — of the verse; artha — the meaning; kahi — I relate; saṅkṣepera — of conciseness; sāra — the pith; bhaktera — of the devotee; icchāya — by the desire; kṛṣṇera — of Lord Kṛṣṇa; sarva — all; avatāra — incarnations.
Translation: 
The essence of the meaning of this verse is that Lord Kṛṣṇa appears in all His innumerable eternal forms because of the desires of His pure devotees.