Self-realization is possible in the human form of life, but not in other forms. There are 8,400,000 species, or forms of life, of which the human form qualified by brahminical culture presents the only chance to obtain knowledge of transcendence. Brahminical culture includes truthfulness, sense control, forbearance, simplicity, full knowledge and full faith in God. It is not that one simply becomes proud of his high parentage. Just as being born the son of a big man affords one a chance to become a big man, so being born the son of a brāhmaṇa gives one a chance to become a brāhmaṇa. But such a birthright is not everything, for one still has to attain the brahminical qualifications for himself. As soon as one becomes proud of his birth as the son of a brāhmaṇa and neglects to acquire the qualifications of a real brāhmaṇa, he at once becomes degraded and falls from the path of self-realization. Thus his life's mission as a human being is defeated.
In the Bhagavad-gītā (6.41-42) we are assured by the Lord that the yoga-bhraṣṭas, or souls fallen from the path of self-realization, are given a chance to rectify themselves by taking birth either in the families of good brāhmaṇas or in the families of rich merchants. Such births afford higher chances for self-realization. If these chances are misused due to illusion, one loses the good opportunity of human life afforded by the almighty Lord.
The regulative principles are such that one who follows them is promoted from the platform of fruitive activities to the platform of transcendental knowledge. After many, many lifetimes of cultivating transcendental knowledge, one becomes perfect when he surrenders unto the Lord. This is the general procedure. But one who surrenders at the very beginning, as recommended in this mantra, at once surpasses all preliminary stages simply by adopting the devotional attitude. As stated in the Bhagavad-gītā (18.66), the Lord at once takes charge of such a surrendered soul and frees him from all the reactions to his sinful acts. There are many sinful reactions involved in karma-kāṇḍa activities, whereas in jñāna-kāṇḍa, the path of philosophical development, the number of such sinful activities is smaller. But in devotional service to the Lord, the path of bhakti, there is practically no chance of incurring sinful reactions. One who is a devotee of the Lord attains all the good qualifications of the Lord Himself, what to speak of those of a brāhmaṇa. A devotee automatically attains the qualifications of an expert brāhmaṇa authorized to perform sacrifices, even though the devotee may not have taken his birth in a brāhmaṇa family. Such is the omnipotence of the Lord. He can make a man born in a brāhmaṇa family as degraded as a lowborn dog-eater, and He can also make a lowborn dog-eater superior to a qualified brāhmaṇa simply on the strength of devotional service.