That is the sign of devotee: appreciation [of] the activities of devotee. This appreciation means a devotee who is actually freed from all
contamination, he does not find any fault with other devotee. That is the sign. He does not think himself that he is bigger devotee or greater devotee than others. He thinks himself as the lowest of all. As Caitanya, as Caitanya-caritamrta author, Kaviraja Gosvami, says, purisera kita haite muni se lagistha: [Cc. Adi 5.205] "I am lower than the insect within the stool." Jagai-madhai haite se muni papistha: "I am greater sinner than Jagai and Madhai." Mora nama yei laya tara punya ksaya: "Anyone who takes my name, immediately, all the result of his pious activities becomes vanquished." He's placing like that. Because it is not imitation or any bluff. He's… Any devotee who's actually advanced, he feels like that. Just like great scientist, Sir Isaac Newton, he used to say that "I have simply collected a few grains of sand in the ocean of knowledge." Yes. He used to say. And actually, that is the fact. Everything is unlimited. So nobody should be proud falsely that he has become a great devotee. Everyone should be very humble.
trnad api sunicena
taror api sahisnuna
amanina manadena
kirtaniyah sada harih
 [Cc. Adi 17.31]
If one thinks that he has become very advanced in devotion, then that is very dangerous.

(From Srila Prabhupada's lecture on The Nectar of Devotion — November 11, 1972, Vrndavana)