CC Ādi 6.100
ātmā haite kṛṣṇera bhakta haya premāspada
The conception of oneness with the Supreme Personality of Godhead is inferior to that of eternal service to the Lord because Lord Kṛṣṇa is more affectionate to devotees than to His personal self. In Śrīmad-Bhāgavatam (9.4.68) the Lord clearly says:
sādhavo hṛdayaṁ mahyaṁ sādhūnāṁ hṛdayaṁ tv aham
mad anyat te na jānanti nāhaṁ tebhyo manāg api
“The devotees are My heart, and I am the heart of My devotees. My devotees do not know anyone but Me; similarly, I do not know anyone but My devotees.” This is the intimate relationship between the Lord and His devotees.