The seriously inquisitive student or sage, well equipped with knowledge and detachment, realizes that Absolute Truth by rendering devotional service in terms of what he has heard from the Vedānta-śruti.
The Absolute Truth is realized in full by the process of devotional service to the Lord, Vāsudeva, or the Personality of Godhead, who is the full-fledged Absolute Truth. Brahman is His transcendental bodily effulgence, and Paramātmā is His partial representation. As such, Brahman or Paramātmā realization of the Absolute Truth is but a partial realization. There are four different types of human beings—the karmīs, the jñānīs, the yogīs and the devotees. The karmīs are materialistic, whereas the other three are transcendental. The first-class transcendentalists are the devotees who have realized the Supreme Person. The second-class transcendentalists are those who have partially realized the plenary portion of the absolute person. And the third-class transcendentalists are those who have barely realized the spiritual focus of the absolute person. As stated in the Bhagavad-gītā and other Vedic literatures, the Supreme Person is realized by devotional service, which is backed by full knowledge and detachment from material association. We have already discussed the point that devotional service is followed by knowledge and detachment from material association. As Brahman and Paramātmā realization are imperfect realizations of the Absolute Truth, so the means of realizing Brahman and Paramātmā, i.e., the paths of jñāna and yoga, are also imperfect means of realizing the Absolute Truth. Devotional service, which is based on the foreground of full knowledge combined with detachment from material association and which is fixed by the aural reception of the Vedānta-śruti, is the only perfect method by which the seriously inquisitive student can realize the Absolute Truth. Devotional service is not, therefore, meant for the less intelligent class of transcendentalist. There are three classes of devotees, namely first, second, and third class. The third-class devotees, or the neophytes, who have no knowledge and are not detached from material association, but who are simply attracted by the preliminary process of worshiping the Deity in the temple, are called material devotees. Material devotees are more attached to material benefit than transcendental profit. Therefore, one has to make definite progress from the position of material devotional service to the second-class devotional position. In the second-class position, the devotee can see four principles in the devotional line, namely the Personality of Godhead, His devotees, the ignorant and the envious. One has to raise himself at least to the stage of a second-class devotee and thus become eligible to know the Absolute Truth.
A third-class devotee, therefore, has to receive the instructions of devotional service from the authoritative sources of Bhāgavata. The number one Bhāgavata is the established personality of devotee, and the other Bhāgavatam is the message of Godhead. The third-class devotee therefore has to go to the personality of devotee in order to learn the instructions of devotional service. Such a personality of devotee is not a professional man who earns his livelihood by the business of Bhāgavatam. Such a devotee must be a representative of Śukadeva Gosvāmī, like Sūta Gosvāmī, and must preach the cult of devotional service for the all-around benefit of all people. A neophyte devotee has very little taste for hearing from the authorities. Such a neophyte devotee makes a show of hearing from the professional man to satisfy his senses. This sort of hearing and chanting has spoiled the whole thing, so one should be very careful about the faulty process. The holy messages of Godhead, as inculcated in the Bhagavad-gītā or in the Śrīmad-Bhāgavatam, are undoubtedly transcendental subjects, but even though they are so, such transcendental matters are not to be received from the professional man, who spoils them as the serpent spoils milk simply by the touch of his tongue.
A sincere devotee must, therefore, be prepared to hear the Vedic literature like the Upaniṣads, Vedānta and other literatures left by the previous authorities or Gosvāmīs, for the benefit of his progress. Without hearing such literatures, one cannot make actual progress. And without hearing and following the instructions, the show of devotional service becomes worthless and therefore a sort of disturbance in the path of devotional service. Unless, therefore, devotional service is established on the principles of śruti, smṛti, purāṇa or pañcarātra authorities, the make-show of devotional service should at once be rejected. An unauthorized devotee should never be recognized as a pure devotee. By assimilation of such messages from the Vedic literatures, one can see the all-pervading localized aspect of the Personality of Godhead within his own self constantly. This is called samādhi.
(Srimad Bhagavatam----1:2:12----translation and purport).

The Lord gives protection to all living beings because He is their supreme leader. The Vedic hymns confirm that the Lord is the Supreme Person amongst all personalities. The difference between the two living beings is that the one, the Personality of Godhead, provides for all other living beings, and by knowing Him one can achieve eternal peace (Kaṭha Upaniṣad). Such protection is given by His different potencies to different grades of living beings. But as far as His unalloyed devotees are concerned, He gives the protection personally. Therefore, Mahārāja Parīkṣit is protected from the very beginning of his appearance in the womb of his mother. And because he is especially given protection by the Lord, the indication must be concluded that the child would be a first-grade devotee of the Lord with all good qualities. There are three grades of devotees, namely the mahā-bhāgavata, madhyam-adhikārī and the kaniṣṭha-adhikārī. Those who go to the temples of the Lord and offer worshipful respect to the Deity without sufficient knowledge in the theological science and therefore without any respect for the devotees of the Lord are called materialistic devotees, or kaniṣṭha-adhikārī, the third-grade devotees. Secondly, the devotees who have developed a mentality of genuine service to the Lord and who thus make friendships only with similar devotees, show favor to the neophytes and avoid the atheists are called the second-grade devotees. But those who see everything in the Lord or everything of the Lord and also see in everything an eternal relation of the Lord, so that there is nothing within their purview of sight except the Lord, are called the mahā-bhāgavatas, or the first-grade devotees of the Lord. Such first-grade devotees of the Lord are perfect in all respects. A devotee who may be in any of these categories is automatically qualified by all good qualities, and thus a mahā-bhāgavata devotee like Mahārāja Parīkṣit is certainly perfect in all respects. And because Mahārāja Parīkṣit took his birth in the family of Mahārāja Yudhiṣṭhira, he is addressed herein as the mahā-bhāgavata, or the greatest of the fortunates. The family in which a mahā-bhāgavata takes his birth is fortunate because due to the birth of a first-grade devotee the members of the family, past, present and future up to one hundred generations, become liberated by the grace of the Lord, out of respect for His beloved devotee. Therefore, the highest benefit is done to one's family simply by becoming an unalloyed devotee of the Lord.
(Srimad Bhagavatam----1:12:17---- purport).

"A person who is always chanting the holy name of the Lord is to be considered a first-class Vaiṣṇava, and your duty is to serve his lotus feet."
Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura says that any Vaiṣṇava who is constantly chanting the holy name of the Lord should be considered to have attained the second platform of Vaiṣṇavism. Such a devotee is superior to a neophyte Vaiṣṇava who has just learned to chant the holy name of the Lord. A neophyte devotee simply tries to chant the holy name, whereas the advanced devotee is accustomed to chanting and takes pleasure in it. Such an advanced devotee is called a madhyama-bhāgavata, which indicates that he has attained the intermediate stage between the neophyte and the perfect devotee. Generally a devotee in the intermediate stage becomes a preacher. A neophyte devotee or an ordinary person should worship the madhyama-bhāgavata, who is a via medium.
In his Upadeśāmṛta (5) Śrīla Rūpa Gosvāmī says, praṇatibhiś ca bhajantam īśam. This means that madhyama-adhikārī devotees should exchange obeisances between themselves.
The word nirantara, meaning "without cessation, continuously, constantly," is very important in this verse. The word antara means "interval." If one has desires other than a desire to perform devotional service—in other words, if one sometimes engages in devotional service and sometimes strives for sense gratification—his service will be interrupted. A pure devotee, therefore, should have no desire other than to serve Kṛṣṇa. He should be above fruitive activity and speculative knowledge. In his Bhakti-rasāmṛta-sindhu (Bhakti-rasāmṛta-sindhu 1.1.11), Śrīla Rūpa Gosvāmī says:
anyābhilāṣitā-śūnyaṁ jñāna-karmādy-anāvṛtam
ānukūlyena kṛṣṇānu-śīlanaṁ bhaktir uttamā
(CC.2:19:167)
This is the platform of pure devotional service. One should not be motivated by fruitive activity or mental speculation but should simply serve Kṛṣṇa favorably. That is first-class devotion.
Another meaning of antara is "this body." The body is an impediment to self-realization because it is always engaged in sense gratification. Similarly, antara means "money." If money is not used in Kṛṣṇa's service, it is also an impediment. Antara also means janatā, "people in general." The association of ordinary persons may destroy the principles of devotional service. Similarly, antara may mean "greed"—greed to acquire more money or enjoy more sense gratification. Finally, the word antara may also mean "atheistic ideas," by which one considers the temple Deity to be made of stone, wood or gold. All of these are impediments. The Deity in the temple is not material—He is the Supreme Personality of Godhead Himself. Similarly, considering the spiritual master an ordinary human being (guruṣu nara-matiḥ) is also an impediment. Nor should one consider a Vaiṣṇava a member of a particular caste or nation. Nor should a Vaiṣṇava be considered material. Caraṇāmṛta should not be considered ordinary drinking water, and the holy name of the Lord should not be considered an ordinary sound vibration. Nor should one look on Lord Kṛṣṇa as an ordinary human being, for He is the origin of all viṣṇu-tattvas; nor should one regard the Supreme Lord as a demigod. Intermingling the spiritual with the material causes one to look on transcendence as material and the mundane as spiritual. This is all due to a poor fund of knowledge. One should not consider Lord Viṣṇu and things related to Him as being different. All this is offensive.
In the Bhakti-sandarbha (265), Śrīla Jīva Gosvāmī writes: nāmaikaṁ yasya vāci smaraṇa-patha-gatam ity-ādau deha-draviṇādi-nimittaka-"pāṣaṇḍa"-śabdena ca daśa aparādhā lakṣyante, pāṣaṇḍa-mayatvāt teṣām. "In the verse beginning nāmaikaṁ yasya, we find the word pāṣaṇḍa ("godlessness"). The word literally indicates misuse of one's body or property, but in that verse it implies the ten offenses against the Lord's holy name, since each of these leads to such godless behavior."
The Māyāvādīs look on Viṣṇu and Vaiṣṇavas imperfectly due to their poor fund of knowledge, and this is condemned. In Śrīmad-Bhāgavatam (11.2.46), the intermediate Vaiṣṇava is described as follows:
īśvare tad-adhīneṣu bāliśeṣu dviṣatsu ca
prema-maitrī-kṛpopekṣā yaḥ karoti sa madhyamaḥ
"The intermediate Vaiṣṇava has to love God, make friends with the devotees, instruct the innocent and reject jealous people. These are the four functions of the Vaiṣṇava in the intermediate stage." In the Caitanya-caritāmṛta (CC.2:22:64) Śrī Sanātana Gosvāmī is taught:
śraddhāvān jana haya bhakti-adhikārī
"uttama", "madhyama", "kaniṣṭha"—śraddhā-anusārī
"One who is faithful is a proper candidate for devotional service. In terms of one's degree of faith in devotional service, one is a first-class, second-class or neophyte Vaiṣṇava."
śāstra-yukti nāhi jāne dṛḍha, śraddhāvān
"madhyama-adhikārī" sei mahā-bhāgyavān
"One who has attained the intermediate stage is not very advanced in śāstric knowledge, but he has firm faith in the Lord. Such a person is very fortunate to be situated on the intermediate platform." (CC.2:22:67)
rati-prema-tāratamye bhakta-taratama
"Attraction and love for God are the ultimate goal of devotional service. The degrees of such attraction and love distinguish the different stages of devotion—neophyte, intermediate and perfectional." (CC.2:22:71) An intermediate devotee is greatly attracted to chanting the holy name, and by chanting he is elevated to the platform of love. If one chants the holy name of the Lord with great attachment, he can understand his position as an eternal servant of the spiritual master, other Vaiṣṇavas and Kṛṣṇa Himself. Thus the intermediate Vaiṣṇava considers himself kṛṣṇa-dāsa, Kṛṣṇa's servant. He therefore preaches Kṛṣṇa consciousness to innocent neophytes and stresses the importance of chanting the Hare Kṛṣṇa mahā-mantra. An intermediate devotee can identify the nondevotee or motivated devotee. The motivated devotee or the nondevotee are on the material platform, and they are called prākṛta. The intermediate devotee does not mix with such materialistic people. However, he understands that the Supreme Personality of Godhead and everything related to Him are on the same transcendental platform. Actually none of them are mundane.
(Sri Caitanya Caritamrta----2:16:72----translation).