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.
When we face difficulties and still remain faithful to Krishna and the spiritual master, we access the infinite mercy of their hearts.
To travel in another country, you need visa permission, similarly to go back to Godhead you need permission & mercy from his pure devotee.
Our own endeavours can only take us to a certain level but ultimate goal will be attained only by the mercy of Vaishnavas and mercy of Krishna.