By His Divine Grace A. C. Bhaktivedānta Swami Prabhupāda
Hrda means heart, and su means good, good heart. A devotee, a mahatma, is a good heart. How is he a good heart? He sees everyone that “This living entity,” especially human being, “he is engrossed in the clutches of maya. He is suffering. Let me try to make him understand Krishna consciousness, or his eternal relationship with Krishna.” He tries everywhere. That is his business. He doesn’t mind whether he is a failure. Failure or success, he doesn’t mind. But he thinks, “Oh, this conditioned soul is suffering. Let me do something.” vānchā-kalpa-tarubhyaś ca krpā-sindhubhya eva ca: Therefore the Vaishnava (devotee of Krishna) is just like an ocean of mercy. He always feels for the sufferings of the humanity. That is his business. People think that the devotees have taken relief from all social work. But a Vaishnava is giving the best social service because he knows what is the cause of suffering and how people can be saved. Therefore he is suhrdah. Suhrdah means well-wisher friend. A Vaishnava or spiritual master or a saintly person is suhrdah. Suhrdah means he is well-wisher friend. As Krishna is suhrdah, the friend of all living entities (suhrdam sarva-bhūtānām, Bg 5.29), similarly, a Vaishnava, Krishna’s devotee, is also suhrdah. And sādhava means well-behaved. 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, if he follows his instruction, it should be understood that it is sure and certain that he is going to Krishna without any fail.
[An excerpt from a lecture delivered on September 14, 1969 in London]