Śrīla Jīva Gosvāmī, in his thesis Bhakti-sandarbha (202), has stated that uncontaminated devotional service is the objective of pure Vaiṣṇavas and that one has to execute such service in the association of other devotees. By associating with devotees of Lord Kṛṣṇa, one develops a sense of Kṛṣṇa consciousness and thus becomes inclined toward the loving service of the Lord. This is the process of approaching the Supreme Lord by gradual appreciation in devotional service. If one desires unalloyed devotional service, one must associate with devotees of Śrī Kṛṣṇa, for by such association only can a conditioned soul achieve a taste for transcendental love and thus revive his eternal relationship with Godhead in a specific manifestation and in terms of the specific transcendental mellow (rasa) that one has eternally inherent in him.
(Sri Caitanya Caritamrta----1:1:35----purport).

If one poses himself as an ācārya but does not have an attitude of servitorship to the Lord, he must be considered an offender, and this offensive attitude disqualifies him from being an ācārya. The bona fide spiritual master always engages in unalloyed devotional service to the Supreme Personality of Godhead. By this test he is known to be a direct manifestation of the Lord and a genuine representative of Śrī Nityānanda Prabhu. Such a spiritual master is known as ācāryadeva. Influenced by an envious temperament and dissatisfied because of an attitude of sense gratification, mundaners criticize a real ācārya. In fact, however, a bona fide ācārya is nondifferent from the Personality of Godhead, and therefore to envy such an ācārya is to envy the Personality of Godhead Himself. This will produce an effect subversive of transcendental realization.
(Sri Caitanya Caritamrta----1:1:46----purport).

One who is engaged in unalloyed devotional service to the Lord is already situated in the spiritual world (brahma-bhūyāya kalpate). In all circumstances, his activities and dealings with Kṛṣṇa are transcendental and thus not understandable by mundane moralists. It is therefore better not to discuss such activities among mundane people. It is better to give them the Hare Kṛṣṇa mahā-mantra so that they will be gradually purified and then come to understand the transcendental activities of Kṛṣṇa.
(Sri Caitanya Caritamrta----2:4:134----purport).

A brāhmaṇa may be a very learned scholar, but this does not mean that he is free from material contamination. A brāhmaṇa's contamination, however, is in the mode of goodness. In the material world, the three modes are goodness, passion and ignorance, and all of these are simply different gradations of contamination. Unless a brāhmaṇa transcends such contamination and approaches the platform of unalloyed devotional service, he cannot be accepted as a Vaiṣṇava. An impersonalist may be aware of the impersonal Brahman feature of the Absolute Truth, but his activities are on the impersonal platform. Sometimes he imagines a form of the Lord (saguṇa-upāsanā), but such an attempt is never successful in helping one attain complete realization.
(Sri Caitanya Caritamrta----2:15:277----purport).

In Stotra-ratna (46), Yāmunācārya writes: "My Lord, those who keep themselves independent of Your service are helpless. They work on their own account, and they receive no support from superior authority. Therefore I long for the time when I shall engage fully in Your transcendental loving service without any desire for material satisfaction and without being confined to the mental plane. Only when I engage in such unalloyed devotional service will I enjoy actual spiritual life."
(Teachings of Lord Caitanya).

In the Nāradīya Purāṇa there is a statement about development of ecstatic love simply by speaking. Lord Kṛṣṇa said to Nārada, "O best of the brāhmaṇas, I wish that you may developunalloyed devotional service to Me, which is full of transcendental bliss and all auspiciousness."
In the Skanda Purāṇa there is a statement about developing ecstatic love toward Kṛṣṇa simply by glancing. It is stated there, "When the inhabitants of Jāṅgala Province saw the Personality of Godhead, Kṛṣṇa, they were so stricken with feeling that they could not withdraw their glance from Him."
(Nectar of Devotion).

In the Nārada-pañcarātra pure, unalloyed devotional service is explained as being without any motive for personal benefit. If a devotee is continuously in love with Lord Kṛṣṇa and his mind is always fixed upon Him, that devotional attitude will prove to be the only means of attracting the attention of the Lord. In other words, a Vaiṣṇava who is incessantly thinking of the form of Lord Kṛṣṇa is to be known as a pure Vaiṣṇava.
(Nectar of Devotion).