Sree Sree Guru Gaurangau Jayatah!
What are the original qualities of a sadhu? One is, one-pointed devotion to the Supreme Lord and another is, that you have to give up this varnasrama-dharma and bodily relations for the service of Sri Krishna. If you do this, then you are doing good to all. That is a sadhu. Another original quality of a sadhu is that he only likes to hear and speak about Krishna:
mad-asrayah katha mrstah
srnvanti kathayanti ca
tapanti vividhas tapa
naitan mad-gata-cetasah
(Srimad Bhagavatam, 3.25.23)
Why does the sadhu wish only to hear and speak about Krishna? Because when the sadhu does not have the company of his beloved Supreme Lord, how can he live? How can he survive? He survives by singing the glories of the Supreme Lord, always hearing about and remembering Him. That is the life and soul of a sadhu. No sadhu can survive without hearing and speaking about Krishna. It is like water to a fish. A fish cannot remain without water. Like that, without hearing about Krishna, without speaking about Krishna, without remembering Krishna, a sadhu cannot survive. That is his very life. That quality must be present in him. Having separation grief, he cannot remain without speaking about Krishna. That quality you must clearly be able to see—whether or not he has the taste to hear and speak about Krishna's name, form, attributes, etc.
---Jagad-guru His Divine Grace Srila Bhakti Ballabh Tirtha Goswami Maharaj