To recognise a Vaiṣṇava, you should know the nature of a Vaiṣṇava. One can know that nature only by observing two particular actions. Those who are deceitful try to establish themselves by concealing their nature, but such imitation does not last. Within two to four days they are compelled to reveal their real nature. What is the nature of a Vaiṣṇava? The answer is that the nature of a Vaiṣṇava is the nature of a great personality as described in the śāstra. Śrī Caritāmṛta says –
mahānubhāvera cittera svabhāva ei haya
puṣpa-sama komala kaṭhina vajra-maya
(“The natural heart of a great personality is soft just like a flower and as hard as a thunderbolt.” – Caitanya-caritāmṛta, Madhya-līlā 7.72)
In regards to those things that are favorable towards bhajana, the heart of a great personality is as soft as a flower. The heart of a great personality becomes soft when he notices those things that are beneficial for bhajana such as certain objects, time, circumstances and places. The mind of a great personality is as hard as a thunderbolt when he considers those objects, time, conditions and places that are unfavorable for bhajana. He does not accept any of these things for himself. The heart of a Vaiṣṇava becomes soft upon seeing the sufferings of the jīvas, but when he sees a jīva’s hatred towards Vaiṣṇavas or his hatred towards bhagavat-bhakti, he becomes hard towards such jīvas and ignores them. As long as his family is favourable towards bhajana, he is very soft-hearted towards his wife and son. When the family becomes hostile towards bhajana, his heart becomes hard and he says goodbye to his wife and son forever. His heart is softened with friendship when he sees true dharma. His heart sinks and becomes just like a thunderbolt when he sees opposition towards true dharma. When this astonishing nature is noticed in a human being, that great personality is a Vaiṣṇava.