The prime qualifications of a devotee Sadhu are mentioned in the Chaitanya Charitamrita. It is said there that a ‘Sadhu’ has innumerable good qualifications but primarily a ‘Sadhu’ is always found to have possessed the following signs of goodness. He is (1) kind, (2) tolerant, (3) truthful, (4) equal, (5) stainless, (6) liberal, (7) mild, (8) clean, (9) meek, (10) altruist, (11) peaceful, (12) self-surrendered to Krishna, (13) satisfied, (14) humble, (15) fixed up (16) self-restrained, (17) frugal, (18) sagacious, (19) respectful (20) simple, (21) grave, (22) compassionate, (23) friendly, (24) poetic, (25) expert and (26) silent.
Bhagwat Geeta has not nullified all the above mentioned primary twenty six qualifications of a ‘Sadhu’ by the statement even if a man is accustomed to vicious habits.’ The idea is explained in the following sloka in which it is said that such well-settled devotee shall soon be well-qualified with all the pious qualifications of a ‘Sadhu’. But because one has become faithfully fixed up in the service of the Lord the seed of all godly qualifications is sowed therein and the resultant fortification will come in vogue, without delay. And therefore the primary qualification of a ‘Sadhu’ is that he must be an unflinching devotee of the Lord.