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.
Out of many millions of wandering living entities, one who is very fortunate gets an opportunity to associate with a bonafide spiritual master by the grace of Krishna. By the mercy of both Krishna and the spiritual masters, such a person receives the seed of the creeper of devotional service.
The Lord is always worthy to be the master of the surrendered soul, for He is the ocean of mercy.
Srimad Bhagavatam 4.8.46,