CC Madhya 8.285
tomā vinā ei-rūpa nā dekhe anya-jana
After embracing Rāmānanda Rāya, the Lord pacified him, informing him, “But for you, no one has ever seen this form.”
In the Bhagavad-gītā (7.25) Lord Kṛṣṇa states:
mūḍho ’yaṁ nābhijānāti loko mām ajam avyayam
“I am never manifest to the foolish and unintelligent. For them I am covered by My internal potency [yogamāyā], and so they do not know Me, who am unborn and infallible.”
The Lord always reserves the right of not being exposed to everyone. The devotees, however, are always engaged in the service of the Lord, serving with the tongue by chanting the Hare Kṛṣṇa mantra and tasting mahā-prasādam. Gradually the sincere devotee pleases the Supreme Personality of Godhead, and the Supreme Lord reveals Himself. One cannot see the Supreme Lord by making personal efforts. Rather, when the Lord is pleased by the service of a devotee, He reveals Himself.