There are different modes of material nature, and all mundane functions in which a common man is very much interested or in which he takes part become unattractive for the devotee. This state of affairs is described herein as pratinivṛtta-guṇormi, and it is possible by ātma-prasāda, or complete self-satisfaction without any material connection. The first-class devotee of the Lord attains this stage by devotional service, but despite his loftiness, for the Lord's satisfaction he may play the voluntary part of a preacher of the Lord's glory and dovetail all into devotional service, even mundane interest, just to give the neophytes a chance to transform mundane interest into transcendental bliss.
(Srimad Bhagavatam----2:3:12----purport).

The first-class devotee does not at all see anyone who is not in the service of the Lord, but the second-class devotee makes distinctions between devotees and nondevotees.
(Srimad Bhagavatam----2:3:21----purport).

Sometimes the first-class devotee also comes down to the category of the second-class devotee for preaching work.
(Srimad Bhagavatam----2:3:21----purport).

The first-class devotee gives assurance to every living being that there is no fear of this material existence: "Let us live in Kṛṣṇa consciousness and conquer the nescience of material existence."
(Srimad Bhagavatam----3:21:31----purport).

Unless one is very intelligent, one cannot take to devotional service, or Kṛṣṇa consciousness. Naturally, anyone who is a first-class devotee must be a first-class intelligent person and therefore not interested in any kind of benediction within this material world.
(Srimad Bhagavatam----4:12:8----purport).

Kṛṣṇa consciousness, however, provides first-class training for a man or a woman. A man should be trained to be a first-class devotee of Lord Kṛṣṇa, and a woman should be trained to be a very chaste follower of her husband. That will make the lives of both of them happy.
(Srimad Bhagavatam----6:18:42----purport).

One has to learn humility and meekness at home, following the instructions of Śrī Caitanya Mahāprabhu, and in that way one's life will be spiritually successful. One should not try to be an artificially advanced devotee, thinking, "I am a first-class devotee." Such thinking should be avoided.
(Sri Caitanya Caritamrta----2:7:130----purport).

Unless one is a first-class devotee, he cannot be a preacher. A preacher is generally a topmost devotee, but in order to meet the general populace, he has to come to distinguish between devotees and nondevotees.
(Sri Caitanya Caritamrta----2:8:44----purport).

Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura says that if an observer immediately remembers the holy name of Kṛṣṇa upon seeing a Vaiṣṇava, that Vaiṣṇava should be considered a mahā-bhāgavata, a first-class devotee. Such a Vaiṣṇava is always aware of his Kṛṣṇa conscious duty, and he is enlightened in self-realization.
(Sri Caitanya Caritamrta----2:16:74----purport).

The neophyte and intermediate devotees can gradually rise to the platform of uttama-adhikārī and become first-class devotees. Symptoms of a first-class devotee are given in Śrīmad-Bhāgavatam (11.2.45):
sarva-bhūteṣu yaḥ paśyed bhagavad-bhāvam ātmanaḥ
bhūtāni bhagavaty ātmany eṣa bhāgavatottamaḥ
"The most advanced devotee sees within everything the soul of all souls, the Supreme Personality of Godhead, Śrī Kṛṣṇa. Consequently, he sees systematically everything in relation to the Supreme Lord and understands that everything that exists is eternally situated within the Lord."
(Sri Caitanya Caritamrta----2:16:74----purport).

“One whose faith is soft and pliable is called a neophyte, but by gradually following the process he will rise to the platform of a first-class devotee."
(Sri Caitanya Caritamrta----2:22:69----purport).

A first-class devotee has firm conviction in the revealed scriptures and is expert in arguing according to the śāstras. He is firmly convinced of the science of Kṛṣṇa consciousness.
(Sri Caitanya Caritamrta----2:22:71----purport).

The second-class devotee, even though he cannot support his position with śāstric reference, can gradually become a first-class devotee by studying the śāstras and associating with a first-class devotee. However, if the second-class devotee does not advance himself by associating with a first-class devotee, he makes no progress. There is no possibility that a first-class devotee will fall down, even though he may mix with nondevotees to preach. Conviction and faith gradually increase to make one an uttama-adhikārī, a first-class devotee.
(Sri Caitanya Caritamrta----2:22:71----purport).

Devotional service is so enchanting that even the first-class devotees (uttama-adhikārīs) also come down to the second platform to preach and render service to the Lord for the benefit of the whole world.
(Sri Caitanya Caritamrta----2:24:205----purport).

That the Lord is represented in everyone's heart is a fact, and therefore the highly advanced devotee offers his respects to every living entity, considering that the body is the temple of the Lord. But it is not possible for all men to come to that stage of life immediately, because that stage is for the first-class devotee.
(Krsna Book).

In Śrīmad-Bhāgavatam (11.2.55) the relationship between the devotee and the Supreme Lord is confirmed as follows:
viṣṛjati hṛdayaṁ na yasya sākṣād
dharir avaśābhihito 'py aghaugha-nāśaḥ
praṇaya-raśanayā dhṛtāṅghri-padmaḥ
sa bhavati bhāgavata-pradhāna uktaḥ
"If a person's heart is always tied to the lotus feet of the Supreme Lord with the rope of love, the Lord does not leave him. Indeed, even if his remembrance is not perfect, he is to be considered a first class devotee."
(Teachings of Lord Caitanya).

He understands perfectly that the ultimate goal of life is to attain to the transcendental loving service of Kṛṣṇa, and he knows that Kṛṣṇa is the only object of worship and love. This first-class devotee is one who has strictly followed the rules and regulations under the training of a bona fide spiritual master and has sincerely obeyed him in accord with revealed scriptures. Thus, being fully trained to preach and become a spiritual master himself, he is considered first class. The first-class devotee never deviates from the principles of higher authority, and he attains firm faith in the scriptures by understanding with all reason and arguments. When we speak of arguments and reason, it means arguments and reason on the basis of revealed scriptures. The first-class devotee is not interested in dry speculative methods meant for wasting time. In other words, one who has attained a mature determination in the matter of devotional service can be accepted as the first-class devotee.
(Nectar of Devotion).

Due to constant engagement in devotional service—hearing, chanting, remembering, worshiping the Deity, etc., as prescribed in nine varieties—there are different symptoms which appear in the body of a devotee. These eight bodily transformations, which indicate that a devotee is already liberated within himself, are called aṣṭa-sāttvika-vikāra (cc.3:14:99). When a devotee completely forgets his bodily existence, he should be understood to be liberated. He is no longer encaged in the body. The example is given that when a coconut becomes completely dry, the coconut pulp within the coconut shell separates from the bondage of the shell and the outer covering. By moving the dry coconut, one can hear that the pulp within is no longer attached to the shell or to the covering. Similarly, when one is fully absorbed in devotional service, he is completely disconnected from the two material coverings, the subtle and gross bodies. Dhruva Mahārāja actually attained this stage of life by constantly discharging devotional service. He has already been described as a mahā-bhāgavata, for unless one becomes a mahā-bhāgavata, or a first-class pure devotee, these symptoms are not visible. Lord Caitanya exhibited all these symptoms. Ṭhākura Haridāsa also exhibited them, and there are many pure devotees who manifested such bodily symptoms. They are not to be imitated, but when one is actually advanced, these symptoms are exhibited. At that time it is to be understood that a devotee is materially free. Of course, from the beginning of devotional service the path of liberation immediately opens, just as the coconut taken from the tree immediately begins to dry; it simply takes some time for the shell and pulp to separate from one another.
(Srimad Bhagavatam----4:12:18----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).