Krishna Book 2-31 — Although You are constantly with the conditioned soul, only when he becomes purified by devotional service do You become revealed to him. Others, who are bewildered by fruitive activities, either by Vedic injunction or customary dealings, and who do not take to devotional service, become captivated by the external happiness of the bodily concept of life. You are not revealed to such persons. Rather, You remain far, far away from them. But for one who, being engaged in Your devotional service, has purified his heart by constant chanting of Your holy name, You become very easily understood as his eternal constant companion.
"It is said that Your Lordship, sitting in the heart of a devotee, gives him direction by which he can very quickly come back to home, back to You. This direct dictation by You reveals Your existence within the heart of the devotee. Only a devotee can immediately appreciate Your existence within his heart, whereas for a person who has only a bodily conception of life and is engaged in sense gratification You always remain covered by the curtain of yogamāyā. Such a person cannot realize that You are very near, sitting within his heart.
Adi 1.52 purport — We cannot discover the mysteries of the Lord by our mundane endeavors; they are only revealed, by His grace, to the proper devotees. These mysteries are gradually disclosed to the various grades of devotees in proportion to the gradual development of their service attitude.
ISO 16 purport — As stated in the Katha Upaniṣad (1.2.23), the Lord can be known only by those whom He favors, and not by anyone else. Such special favors are bestowed upon His pure devotees only.
SB 1.13.27 purport — One should therefore practice devotional service at home, hearing and chanting the holy name, quality, form, pastimes, entourage, etc., in association with pure devotees, and this practice will help one awaken God consciousness in proportion to one's sincerity of purpose. One who desires material benefit by such devotional activities can never depend on the Supreme Personality of Godhead, although He sits in everyone's heart. Nor does the Lord give any direction to persons who worship Him for material gain. Such materialistic devotees may be blessed by the Lord with material benefits, but they cannot reach the stage of the first-class human being, as above mentioned.