It is said, therefore, by Vaiṣṇava authorities that even the most intelligent person cannot understand the plans and activities of a pure devotee. The exact words are tāṅra vākya, kriyā, mudrā vijñeha nā bujhaya (Caitanya-caritāmṛta, Madhya 23.39). A person who is thus always engaged in the service of the Lord or is always thinking and planning how to serve the Lord is to be considered completely liberated at present, and in the future his going back home, back to Godhead, is guaranteed. He is above all materialistic criticism, just as Kṛṣṇa is above all criticism.
(Bhagavad-Gita-------9:28-------purport).

According to Bhagavad-gītā (10.9) the characteristics of pure devotees are wonderful. The complete functional activities of a pure devotee are always engaged in the service of the Lord, and thus the pure devotees exchange feelings of ecstasy between themselves and relish transcendental bliss. This transcendental bliss is experienced even in the stage of devotional practice (sādhana-avasthā), if properly undertaken under the guidance of a bona fide spiritual master.
(Srimad Bhagavatam------2:3:12--------purport).

As a pure devotee of the Lord, Arjuna agreed to fight in preference to his own decision, and thus Arjuna fought to assist the Lord in His mission of diminishing the burden of the world. All the activities of a pure devotee are executed on behalf of the Lord because a pure devotee of the Lord has nothing to do for his personal interest. Arjuna's killing was as good as killing by the Lord Himself.
(Srimad Bhagavatam------2:3:20--------purport).

Śrīmad-Bhāgavatam is full of the transcendental topics of the Personality of Godhead and His pure devotees. In the absolute world there is no difference in quality between the Supreme Lord and His pure devotee. Therefore, hearing the topics of the Lord and hearing of the character and activities of the pure devotee have the same result, namely, the development of devotional service.
(Srimad Bhagavatam------3:13:3--------purport).

It is therefore said by a Vaiṣṇava poet, vaiṣṇavera kriyāmudrā vijñe nā bujhāya: no one can understand the activities of a pure devotee. A pure devotee's activities may appear like ordinary activities, but behind them there is profound significance—the satisfaction of the Lord. In order to understand the activities of a Vaiṣṇava, one has to become very expert.
(Srimad Bhagavatam------4:22:50--------purport).

A prākṛta devotee, or neophyte devotee, is still on the material platform. He certainly engages in worshiping the Deity, but he cannot appreciate the activities of a pure devotee. It has actually been seen that even an authorized devotee who is engaged in the service of the Lord by preaching the mission of Kṛṣṇa consciousness is sometimes criticized by neophyte devotees.
(Srimad Bhagavatam------7:14:39--------purport).

One who is not very expert in preaching may chant in a secluded place, avoiding bad association, but for one who is actually advanced, preaching and meeting people who are not engaged in devotional service are not disadvantages. A devotee gives the nondevotees his association but is not affected by their misbehaviour. Thus by the activities of a pure devotee even those who are bereft of love of Godhead get a chance to become devotees of the Lord one day.
(Sri Caitanya Caritamrta-------1:7:92-------purport).