Srimad Bhagavatam (S.B) 3.25.21 explains, “The symptoms of a sadhu are that he is tolerant, merciful and friendly to all living entities. He has no enemies, he is peaceful, he abides by the scriptures, and all his characteristics are sublime.”
A sadhu is a dedicated devotee of the Lord, he spends all his time and energy in continuously chanting Lord’s holy names, extolling his activities and sharing his message to all without any discrimination and without compromising with the principles. He speaks about God fearlessly, tolerates insults without any complain and is ready to take any difficulties to make the world God conscious. The ruffians caned Haridas Thakura at 22 marketplaces, Lord Nityananda was violently attacked by Jagai and Madhai but they not just continued preaching them about God but also prayed to the Supreme Lord to forgive them for their nefarious acts. A sadhu does not hate anyone because he knows that all living entities are parts and parcels of the Lord. “The humble sages, by virtue of true knowledge, see with equal vision a learned and gentle brahmana, a cow, an elephant, a dog and a dog-eater [outcaste].” (Bhagavad Gita 5.18)
A sadhu engages everyone in the service of the Lord. He never says to people, “serve me” but instead asks everyone to “serve Krishna”. Being very compassionate towards all living beings, he is not satisfied by his own liberation but works hard to liberate all.
SB 3.25.22 explains, “.. a sādhu engages in staunch devotional service to the Lord without deviation. For the sake of the Lord he renounces all other connections, such as family relationships and friendly acquaintances within the world.” Without any ulterior motives, any material attachments, any desire for name, fame, money he distributes love of God to all. “O almighty Lord, I have no desire to accumulate wealth, nor do I desire beautiful women, nor do I want any number of followers. I only want your causeless devotional service birth after birth.” Siksastakam 4.
A sadhu never identifies himself with any material designation; he just desires to serve the Lord. Chaitanya Mahaprabhu succinctly sums up the characteristics of a sadhu, He says, “I am not a bahmana, ksatriya, vaisya, sudra, brahmacari or whatever. I am simply the servant of the servant of Krishna.” “Teachings of Lord Kapila, Ch 11, ‘The Symptoms of a Sadhu.’”