To travel in another country, you need visa permission, similarly to go back to Godhead you need permission & mercy from his pure devotee.
A pure devotee of the Lord accepts tribulation as favours from the Lord. Since the Lord is absoulte, there is no mundane difference between the two. (Between tribulation and favours). — Srimad Bhagavatam, 01.09.17.
This is the symptom of a pure devotee. One should serve the spiritual master first. It is not that one should bypass the spiritual master and desire to serve the Supreme Lord. This is not the principle for a Vaishnava.
The big fish, shark, they do not to come into the river. They constantly remain in the ocean. Similarly, those who are pure devotee always remain in the ocean of transcendental loving service to the Lord.
When a pure devotee or spiritual master speak, what he says should be accepted as having been directly spoken by the Supreme Personality of Godhead in the Parampara System. — Sri Caitanya Caritamrita, Antya Lila, 05.71.
Krishna does not agree to award devotional service to merely anyone. Krishna can easily offer a person material happiness or even liberation, but He does not agree very easily to award a person engagement in his devotional service. Devotional service can in fact be attained only through the mercy of a pure devotee. — The Nectar of Devotion, Page 14.