BG Chap 9 - The qualification to understand bhakti
One should be non envious and devoid of the habit of seeing faults in the Lord. Generally the commentators, even if they are highly scholarly, are all envious of Kṛṣṇa, the Supreme Personality of Godhead. Even the most erudite scholars write on Bhagavad-Gītā very inaccurately. Because they are envious of Kṛṣṇa, their commentaries are useless. The commentaries given by devotees of the Lord are bona fide. No one can explain Bhagavad-Gītā or give perfect knowledge of Kṛṣṇa if he is envious. One who criticizes the character of Kṛṣṇa without knowing Him is a fool. Some criticize the Lord saying He is speaking of His own glories, but one who is freed from such envy is qualified to understand bhakti. Thus bhakti is taught only to one who is not selfish or inimical.
One who understands bhakti will have a direct realization of the Lord and be freed from rebirth (saṁsāra) and freed from all obstacles to bhakti.