This is the process of spiritual realization; one has to receive instruction from a bona fide spiritual master. Kardama Muni was Devahūti's husband, but because he instructed her on how to achieve spiritual perfection, he naturally became her spiritual master also. There are many instances wherein the husband becomes the spiritual master. Lord Śiva also is the spiritual master of his consort, Pārvatī. A husband should be so enlightened that he should become the spiritual master of his wife in order to enlighten her in the advancement of Kṛṣṇa consciousness. Generally strī, or woman, is less intelligent than man; therefore, if the husband is intelligent enough, the woman gets a great opportunity for spiritual enlightenment.
(Srimad Bhagavatam---3:24:5---purport).

One who is engaged in devotional service has not the least fear in material existence. This is because the Supreme Personality of Godhead is the Supersoul and friend of everyone. One who knows this secret is actually educated, and one thus educated can become the spiritual master of the world. One who is an actually bona fide spiritual master, representative of Kṛṣṇa, is not different from Kṛṣṇa.
(Srimad Bhagavatam---4:29:51---purport).

Prahlāda Mahārāja is a vivid example of a pure devotee. Someone might argue that since Prahlāda Mahārāja, even though very old, was attached to his family, and specifically to his grandson Bali Mahārāja, how could he be an ideal example? Therefore this verse uses the word praśāntaḥ. A devotee is always sober. He is never disturbed by any conditions. Even if a devotee remains in gṛhastha life and does not renounce material possessions, he should still be understood to be praśānta, sober, because of his pure devotion to the Lord. Śrī Caitanya Mahāprabhu therefore said:
kibā vipra, kibā nyāsī, śūdra kene naya
yei kṛṣṇa-tattva-vettā, sei 'guru' haya
"Whether one is a brāhmaṇa, a sannyāsī or a śūdra-regardless of what he is-he can become a spiritual master if he knows the science of Kṛṣṇa." (CC-2:8:128) Anyone completely aware of the science of Kṛṣṇa, regardless of his status in life, is a guru. Thus Prahlāda Mahārāja is a guru in all circumstances.
(Srimad Bhagavatam---8:19:2---purport).

Although the members of the so-called Hindu society had followed the social customs and formulas, they had practically forgotten to execute their religious principles strictly. But with the presence of Śrī Caitanya Mahāprabhu they actually began following the regulative principles according to His order. That order is still existing, and anywhere and everywhere, in all parts of the world, one can execute it. That order is to become a spiritual master under the direction of Śrī Caitanya Mahāprabhu by following the regulative principles, chanting daily at least sixteen rounds of the Hare Kṛṣṇa mahā-mantra, and preaching the cult of Kṛṣṇa consciousness all over the world. If we adhere to the order of Śrī Caitanya Mahāprabhu, we shall get spiritual strength without a doubt, and we shall be free to preach this cult of the Hare Kṛṣṇa movement and not be hampered by anyone.
(Sri Caitanya Caritamrta---1:17:126---purport).

A spiritual master from the sannyāsa order has very little opportunity to perform arcana, Deity worship, but when one accepts a spiritual master from the transcendental sannyāsīs, the principle of Deity worship is not at all neglected. To implement this conclusion, Śrī Caitanya Mahāprabhu gave us His opinion in the verse kibā vipra kibā nyāsī, etc. This indicates that the Lord understood the weakness of society in its maintaining that only a gṛhastha-brāhmaṇa should be a spiritual master. Śrī Caitanya Mahāprabhu indicated that it does not matter whether the spiritual master is a gṛhastha (householder), a sannyāsī or even a śūdra. A spiritual master simply must be conversant in the essence of the śāstra; he must understand the Supreme Personality of Godhead. Only then can one become a spiritual master. Dīkṣā actually means initiating a disciple with transcendental knowledge by which he becomes freed from all material contamination.
(Sri Caitanya Caritamrta---2:4:111----purport).

At whosever house Śrī Caitanya accepted His alms by taking prasādam, He would convert the dwellers to His saṅkīrtana movement and advise them just as He advised the brāhmaṇa named Kūrma."
The cult of Śrī Caitanya Mahāprabhu is explained here very nicely. One who surrenders to Him and is ready to follow Him with heart and soul does not need to change his location. Nor is it necessary for one to change his status. One may remain a householder, a medical practitioner, an engineer or whatever. It doesn’t matter. One only has to follow the instruction of Śrī Caitanya Mahāprabhu, chant the Hare Kṛṣṇa mahā-mantra and instruct relatives and friends in the teachings of the Bhagavad-gītā and Śrīmad-Bhāgavatam. 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. It is best not to accept any disciples. One has to become purified at home by chanting the Hare Kṛṣṇa mahā-mantra and preaching the principles enunciated by Śrī Caitanya Mahāprabhu. Thus one can become a spiritual master and be freed from the contamination of material life.
(Sri Caitanya Caritamrta---2:7:130---purport).

The Lord then blessed him saying, "Whatever you write, by the grace of Kṛṣṇa, will come out of your heart and will be accepted as you have requested. I will also give you some notes that you can take down. The first and foremost point is that one should accept a bona fide spiritual master. That is the beginning of spiritual life." Lord Caitanya then requested Sanātana Gosvāmī to write down the symptoms of a true guru and the symptoms of a true devotee. The symptoms of a devotee are described in the Padma Purāṇa: A person who is a qualified brāhmaṇa and at the same time has all the symptoms of a devotee can become a spiritual master for all classes of men. Such a devotee and spiritual master must be respected as God Himself. Even though a person may be born in a very respectable brāhmaṇa family, he cannot become a bona fide spiritual master if he is not a devotee of the Lord. One should not mistakenly think that a bona fide spiritual master has to be born in a so-called brāhmaṇa family. The idea is that a spiritual master must be a qualified brāhmaṇa; that is, he must be qualified by his activities.
(Teachings of Lord Caitanya).

A bona fide spiritual master chants the holy names—Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare—and the transcendental sound vibration enters into the ear of the disciple, and if a disciple follows in the footsteps of his spiritual master and chants the holy name with similar respect, he actually comes to worship the transcendental name. When the transcendental name is worshiped by the devotee, the name Himself spreads His glories within the heart of a devotee. When a devotee is perfectly qualified in chanting the transcendental vibration of the holy name, he is quite fit to become a spiritual master and to deliver all the people of the world.
(Teachings of Lord Caitanya).

One's position should be established by personal qualifications and not by birth. For example, if a man is born in a brāhmaṇa family but his personal qualifications are those of a śūdra, he should be accepted as a śūdra. Similarly, if a person is born in a śūdra family but has the qualifications of a brāhmaṇa, he should be accepted as a brāhmaṇa. All śāstric injunctions, as well as the versions of great sages and authorities, establish that a bona fide spiritual master is not necessarily a brāhmaṇa. The only qualification is that he be conversant with the science of Kṛṣṇa, Kṛṣṇa consciousness. That alone makes one perfectly eligible to become a spiritual master. This is the conclusion of Śrī Caitanya Mahāprabhu in His discussions with Rāmānanda Rāya.
(Teachings of Lord Caitanya).

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).