CC Madhya 9.126

tumi sākṣāt sei kṛṣṇa, jāna nija-karma
yāre jānāha, sei jāne tomāra līlā-marma
Word for word: 
tumi — You; sākṣāt — directly; sei — that; kṛṣṇa — the Supreme Personality of Godhead; jāna — You know; nija-karma — Your activities; yāre jānāha — and unto whom You make it known; sei — that person; jāne — knows; tomāra — Your; līlā-marma — the purport of the pastimes.
Translation: 
“You are the Supreme Personality of Godhead, Kṛṣṇa Himself. You know the purport of Your activities, and the person whom You enlighten can also understand Your pastimes.”
Purport: 

The Supreme Personality of Godhead Kṛṣṇa and His pastimes cannot be understood by blunt material senses. One has to purify the senses by rendering transcendental loving service unto the Lord. When the Lord is pleased and reveals Himself, one can understand the transcendental form, name, qualities and pastimes of the Lord. This is confirmed in the Kaṭha Upaniṣad (2.23) and Muṇḍaka Upaniṣad (3.2.3): yam evaiṣa vṛṇute tena labhyas tasyaiṣa ātmā vivṛṇute tanūṁ svām. “Anyone who is favored by the Supreme Personality of Godhead can understand His transcendental name, qualities, form and pastimes.”