The Lord can award anyone and everyone liberation (mukti) from the bondage of material existence, yet He rarely awards the privilege of love of Godhead, as confirmed by Narada (muktim dadhati karhicit sma na bhakti-yogam). This transcendental devotional service of the Lord is so wonderful that the occupation keeps the deserving devotee always rapt in psychological activities, without deviation from the absolute touch. Thus love of Godhead, developed in the heart of the devotee, is a great mystery. Brahmaji previously told Narada that the desires of Brahmaji are never unfulfilled because he is always absorbed in the transcendental loving service of the Lord; nor has he any desire in his heart save and except the transcendental service of the Lord. That is the beauty and mystery of the process of bhakti-yoga. As the Lord’s desire is infallible because He is acyuta, similarly the desires of the devotees in the transcendental service of the Lord are also acyuta, infallible. This is very difficult, however, for the layman to understand without knowledge of the mystery of devotional service, as it is very difficult to know the potency of touchstone. As touchstone is rarely found, a pure devotee of the Lord is also rarely to be seen, even amongst millions of liberated souls (kotisv api mahamune). Out of all kinds of perfections attained by the process of knowledge, yoga perfection in devotional service is the highest of all and the most mysterious also, even more mysterious than the eight kinds of mystic perfection attained by the process of yogic performances. In the Bhagavad-gita (18.64) the Lord therefore advised Arjuna about this bhakti-yoga: sarva-guhyatamam bhuyah, srnu me paramam vacah  “Just hear from Me again about the most confidential part of the instructions in Bhagavad-gita.”

From Srila Prabhupada’s purport to SB 2.9.35