Pure devotee cannot fall down

 “It should be understood that a madhyama-adhikari, a second-class devotee, is fully convinced of Krishna consciousness but cannot support his convictions with sastric reference. A neophyte may fall down by associating with nondevotees because he is not firmly convinced and strongly situated. The second-class devotee, even though he cannot support his position with sastric reference, can gradually become a first-class devotee by studying the sastras and associating with a first-class devotee. However, if the second-class devotee does not advance himself by associating with a first-class devotee, he makes no progress. THERE IS NO POSSIBILITY THAT A FIRST-CLASS DEVOTEE WILL FALL DOWN, EVEN THOUGH HE MAY MIX WITH NONDEVOTEES TO PREACH. Conviction and faith gradually increase to make one anuttama-adhikari, a first-class devotee.”
Sri Caitanya-caritamrta, Madhya-Lila 22.71