"Hṛda means heart, and su means good, good heart. A devotee, a mahātmā, is good heart. How he is good heart? He sees everyone that 'This living entity,' especially human being, 'he is engrossed in the clutches of māyā. He is suffering. Let me try to make him understand Kṛṣṇa consciousness, or his eternal relationship with Kṛṣṇa.' He tries everywhere. That is his business. He doesn't mind whether he is failure. Failure or success, he doesn't mind. But he thinks, 'Oh, this conditioned soul is suffering. Let me do something.' Therefore Vaiṣṇava's prayer is vāñchā-kalpa-tarubhyaś ca kṛpā-sindhubhya eva ca.
A Vaiṣṇava, he is just like the ocean of mercy. He always feels for the sufferings of the humanity. That is their business. People think that they have taken relief from all social work. But a Vaiṣṇava is giving the best social service because he knows what is the cause of suffering, how people can be saved. Therefore he is suhṛdaḥ. Suhṛdaḥ means well-wisher friend. A Vaiṣṇava or spiritual master or a saintly person is suhṛdaḥ. Suhṛdaḥ means he is well-wisher friend. As Kṛṣṇa is suhṛdaḥ, He is the friend of all living entities... Suhṛdaḥ sarva-bhūtānām. In the Bhagavad-gītā you'll find. Similarly, a Vaiṣṇava, Kṛṣṇa's devotee, is also suhṛdaḥ. Suhṛdaḥ sarva-bhūtānām. Suhṛdaḥ. Sādhava. And sādhava means well-behaved. Sādhavaḥ. Sadācāra. His character is firm, without any spot. So these are the qualifications of sādhu, mahātmā, or spiritual master.
So when one is in contact with such person, then the door of liberation is open. If one is in contact with a pure devotee of the Lord, it should be understood, if he follows his instruction, then it is sure and certain that he is going to Kṛṣṇa without any fail."
(Srila Prabhupada Lecture, London, September 14, 1969)