"The transcendental vibration from the mouth of a pure devotee is so powerful that it can revive the living entity's memory of his eternal relationship with the Supreme Personality of Godhead. In our material existence, under the influence of illusory maya, we have almost forgotten our eternal relationship with the Lord, exactly like a man sleeping very deeply who forgets his duties. In the Vedas it is said that every one of us is sleeping under the influence of maya. We must get up from this slumber and engage in the right service, for thus we can properly utilize the facility of this human form of life. As expressed in a song by Thakura Bhaktivinoda, Lord Caitanya says, jiva jaga, jiva jaga. The Lord asks every sleeping living entity to get up and engage in devotional service so that his mission in this human form of life may be fulfilled. This awakening voice comes through the mouth of a pure devotee.
"A pure devotee always engages in the service of the Lord, taking shelter of His lotus feet, and therefore he has a direct connection with the saffron mercy-particles that are strewn over the lotus feet of the Lord. Although when a pure devotee speaks the articulation of his voice may resemble the sound of this material sky, the voice is spiritually very powerful because it touches the particles of saffron dust on the lotus feet of the Lord. As soon as a sleeping living entity hears the powerful voice emanating from the mouth of a pure devotee, he immediately remembers his eternal relationship with the Lord, although up until that moment he had forgotten everything.
"For a conditioned soul, therefore, it is very important to hear from the mouth of a pure devotee, who is fully surrendered to the lotus feet of the Lord without any material desire, speculative knowledge or contamination of the modes of material nature. Every one of us is kuyogi because we have engaged in the service of this material world, forgetting our eternal relationship with the Lord as His eternal loving servants. It is our duty to rise from the kuyoga platform to become suyogis, perfect mystics. The process of hearing from a pure devotee is recommended in all Vedic scriptures, especially by Lord Caitanya Mahaprabhu. One may stay in his position of life -- it does not matter what it is -- but if one hears from the mouth of a pure devotee, he gradually comes to the understanding of his relationship with the Lord and thus engages in His loving service, and his life becomes completely perfect. Therefore, this process of hearing from the mouth of a pure devotee is very important for making progress in the line of spiritual understanding."
(Srimad-Bhagavatam 4.20.25, Purport)