Devotional service to the Supreme Personality of Godhead is explained in the Bhagavad-gītā, where the Lord says that a self-realized person is always in the transcendental state known as brahma-bhūta, which is characterized by joyfulness. When one is self-realized he becomes joyful. In other words, he is free from the material contamination of lamentation and hankering. As long as we are in material existence, we lament for the losses in our life and hanker for that which we do not have. A self-realized person is joyful because he is free from material lamentation and hankering.
A self-realized person also sees all living entities equally. For him, there is no distinction between the higher and lower species of life. It is also stated that a learned man does not distinguish between a wise brāhmaṇa and a dog because he sees the soul within the body, not the external bodily features. Such a perfected, self-realized person becomes eligible to understand bhakti, or devotional service to the Lord.
Bhakti is so sublime that only through bhakti can one understand the constitutional position of the Lord. That is clearly stated in the Bhagavad-gītā (18.55): bhaktyā mām abhijānāti. "One can understand the Supreme Lord through devotional service, and by no other process." There are different processes of understanding the Absolute Truth, but if a person wants to understand the Supreme Lord as He is, he has to take to the process of bhakti-yoga. There are other mystic processes, such as karma-yoga, jñāna-yoga, and dhyāna-yoga, but it is not possible to understand the Supreme Lord, the Personality of Godhead, except through His devotional service. This is confirmed in the Fourth Chapter of the Bhagavad-gītā (4.3), where we learn that Kṛṣṇa spoke the Bhagavad-gītā to Arjuna simply because he was the Lord's devotee and friend. The Bhagavad-gītā teaches the process of bhakti-yoga, and therefore Lord Kṛṣṇa explained it to Arjuna because he was a great devotee. As far as spiritual life is concerned, becoming a devotee of the Lord is the highest perfection.
People are generally misled by the spell of the illusory energy of material nature. There are innumerable living entities within the material nature, and only some of them are human beings. According to the Vedic literature, there are 8,400,000 species of life. In the Padma Purāṇa it is said that there are 900,000 species of life in the water, 2,000,000 species of plants, 1,100,000 species of insects and reptiles, 1,000,000 species of birds, 3,000,000 species of beasts, and only 400,000 species of human beings. So the humans are the least numerous species of all.
All living entities can be divided into two divisions: those that can move and those that are stationary, such as trees. But there are also many further divisions. Some species fly in the air, some live in the water, and some live on the ground. Among the living entities who live on the ground, only 400,000 are human species, and out of these 400,000 human species, many are uncivilized or unclean; they are not up to the standard of proper civilization. From the historical point of view, the Āryans are the most civilized section of human beings, and among the Āryans, the Indians are especially highly cultured. And among the Indians, the brāhmaṇas are the most expert in knowledge of the Vedas.
The Vedic culture is respected all over the world, and there are people everywhere eager to understand it. The highest perfectional stage of understanding Vedic culture is explained in the Bhagavad-gītā, in the Fifteenth Chapter (15.15), where the Lord says that the purpose of all the Vedas is to understand Him (Lord Kṛṣṇa). Fortunate are those who are attracted to the Vedic cultural life.
The Hindus call themselves followers of the Vedas. Some say they follow the Sāma Veda, and some say they follow the Ṛg Veda. Different people claim to follow different sections of the Vedas, but in fact for the most part they are not followers of the Vedas because they do not follow the rules and regulations of the Vedas. Therefore Lord Caitanya says that since the so-called followers of the Vedas perform all kinds of sinful activities, the number of actual followers of the Vedas is very small; and even among this small, exclusive number, most are addicted to the processes described in the Vedas' karma-kāṇḍa section, by which one can elevate oneself to the perfectional stage of economic development.
The strict followers of the karma-kāṇḍa portions of the Vedas perform various sacrifices for worship of different demigods in order to achieve particular material results. Out of many millions of such worshipers, some may actually engage in the process of understanding the Supreme, the Absolute Truth. They are called jñānīs. Perfection for a jñānī lies in attaining the stage of brahma-bhūta, or self-realization. Only after self-realization is attained does the stage of understanding devotional service begin. The conclusion is that one can begin the process of devotional service, or bhakti, when one is actually self-realized. One who is in the bodily concept of existence cannot understand the process of devotional service.
It is for this reason that the Nārada-bhakti-sūtra begins, "Now, therefore, I shall try to explain the process of devotional service." The word "therefore" indicates that this process of devotional service is for the self-realized soul, one who is already liberated. Similarly, the Vedānta-sūtra begins athāto brahma jijñāsā. The word brahma-jijñāsā refers to inquiry into the Supreme Absolute Truth, and it is recommended for those who have been elevated from the lower stage of addiction to the karma-kāṇḍa portion of the Vedas to the position of interest in the jñāna-kāṇḍa portion. Only when a person is perfectly situated in the realization that he is not the body but a spirit soul can he begin the process of bhakti, or devotional service.