SB 1.2.22

ato vai kavayo nityaṁ
 bhaktiṁ paramayā mudā
vāsudeve bhagavati
 kurvanty ātma-prasādanīm
Synonyms: 
ataḥ — therefore; vai — certainly; kavayaḥ — all transcendentalists; nityam — from time immemorial; bhaktim — service unto the Lord; paramayā — supreme; mudā — with great delight; vāsudeve — Śrī Kṛṣṇa; bhagavati — the Personality of Godhead; kurvanti — do render; ātma — self; prasādanīm — that which enlivens.
Translation: 
Certainly, therefore, since time immemorial, all transcendentalists have been rendering devotional service to Lord Kṛṣṇa, the Personality of Godhead, with great delight, because such devotional service is enlivening to the self.
Purport: 

The speciality of devotional service unto the Personality of Godhead Lord Śrī Kṛṣṇa is specifically mentioned herein. Lord Śrī Kṛṣṇa is the svayaṁ-rūpa Personality of Godhead, and all other forms of Godhead, beginning from Śrī Baladeva, Saṅkarṣaṇa, Vāsudeva, Aniruddha, Pradyumna and Nārāyaṇa and extending to the puruṣa-avatāras, guṇa-avatāras, līlā-avatāras, yugāvatāras and many other thousands of manifestations of the Personality of Godhead, are Lord Śrī Kṛṣṇa’s plenary portions and integrated parts. The living entities are separated parts and parcels of the Personality of Godhead. Therefore Lord Śrī Kṛṣṇa is the original form of Godhead, and He is the last word in the Transcendence. Thus He is more attractive to the higher transcendentalists who participate in the eternal pastimes of the Lord. In forms of the Personality of Godhead other than Śrī Kṛṣṇa and Baladeva, there is no facility for intimate personal contact as in the transcendental pastimes of the Lord at Vrajabhūmi. The transcendental pastimes of Lord Śrī Kṛṣṇa are not newly accepted, as argued by some less intelligent persons; His pastimes are eternal and are manifested in due course once in a day of Brahmājī, as the sun rises on the eastern horizon at the end of every twenty-four hours.