The stage of pure devotion is attained by sincerely serving a pure devotee of the Lord. The first condition of devotional service to the Lord is therefore to be a servant of a pure devotee, and this condition is fulfilled by the statement "reception of the dust of the lotus feet of a pure devotee who has also served another pure devotee." That is the way of pure disciplic succession, or devotional paramparā.
(Srimad Bhagavatam-----2:3:23------purport).

This is also confirmed by Prahlāda Mahārāja. Devotional service cannot be practiced by a mental speculator. Devotional service is a special attainment which can be acquired only by a person who has surrendered unto a pure devotee. As confirmed by Prahlāda Mahārāja, mahīyasāṁ pāda-rajo-'bhiṣekaṁ niṣkiñcanānāṁ na vṛṇīta yāvat: "Unless one accepts the dust of the lotus feet of a pure devotee, who is free from all material contamination, one cannot enter into the devotional service of the Lord." (SB 7.5.32)
(Srimad Bhagavatam-----4:24:26------purport).