The devotee always considers himself unqualified. It is the Diksa Guru, or the Siksa Guru, or the Maha Mantra itself that "force" the devotee to deepen his/her Bhajan. They know when the devotee is prepared. And even if the devotee feels unqualified, have no other alternative but to deepen his/her Bhajan passing from Ajata Ruci to Jata Ruci.
As Srila AC Bhaktivedanta Swami Prabhupada explains: "We are forcibly pushed towards ultimate success."
हरे कृष्ण हरे कृष्ण कृष्ण कृष्ण हरे हरे || हरे राम हरे राम राम राम हरे हरे