To travel in another country, you need visa permission, similarly to go back to Godhead you need permission & mercy from his pure devotee.
The causeless mercy of Lord Vishnu is unparalleled, and such mercy is perceived by the devotees only by the grace of the Lord.
Srimad Bagavatam 1.6.31,
To show them special mercy, I, dwelling in their hearts, destroy with the shining lamp of knowledge the darkness born of ignorance.
Bhagavad Gita 10.11,
By the grace of the spiritual master the cloud of the mercy of the Personality of Godhead is brought in, and then only, when the rains of Krishna consciousness fall, can the fire of material existence be extinguished.
Srimad Bhagavatam 3.21.17,
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.