Krishna can be known only by the causeless mercy of the pure devotee and by no other way.
Mercy is always flowing, but everything depends upon our Receptivity.
Service to the Vaishnavas is the most potent formula for getting the mercy of Spiritual Mater and Krishna.
Whatever our destiny is, whatever our Karma is, if we simply accept the mercy of Guru, "Guru Kripa", it can completely liberate us from all of our previous Karmic bondage.
Unless we hear very strictly with great faith to the order of our Spiritual Master, we will not understand what is the mercy of Krishna and how it is coming upon us.
If we actually want spiritual advancement, we have to be willing to perform tapasya to attract the attention of God to show Him we are serious, to show Him that we are depending on His causeless mercy.