Who is a Strict, Serious and Sincere devotee?

Strict – one who sticks to his vows taken without any compromise, like lines drawn on stone.
+Eg. Raghunath das goswami
-Eg. Monkey who took Ekadasi vow not to eat

Serious – Even when there are temptations, distractions, calamities, he does not turn back from his resolve to surrender to Krishna

+Eg. Haridas thakur (temptations), Shukadev (distractions), Prahlad (calamities)

-Eg. Ajamila (temptations), Bharat maharaja (distractions), Indra while fighting with Vrtrasura (calamities)

Sincere – one who has no material motives, no envy, no malice towards other living entities, one who does not blame others for his sufferings.

+Eg. Ambarish maharaja, Parikshit, Prahlad etc.
-Eg. Indra’s attachment to post, Diti’s envy, Dhrtarashtra’s malice towards Bhima, Duryodhana blaming Bhishma and others for failure in war.