CC Madhya 11.52
avaśya karibena kṛpā tomāra upara
As soon as the Bhaṭṭācārya saw the King’s firm determination, he declared, “The Supreme Lord is approached only by pure love. Your love for Śrī Caitanya Mahāprabhu is very, very deep; therefore without a doubt He will be merciful upon you.”
Such determination is the first qualification. As confirmed by Rūpa Gosvāmī (Upadeśāmṛta 3): utsāhān niścayād dhairyāt. One must first have firm determination, firm faith. When one engages in devotional service, he must maintain this firm determination. Then Kṛṣṇa will be pleased with his service. The spiritual master can show the path of devotional service. If the disciple follows the principles rigidly and undeviatingly, he will certainly receive the mercy of Kṛṣṇa. This is confirmed by the śāstras.