click on image to enlarge
The symptoms of a sādhu 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. (SB. 3,25,21)
A sādhu, as described above, is a devotee of the Lord. His concern, therefore, is to enlighten people in devotional service to the Lord. That is his mercy. He knows that without devotional service to the Lord, human life is spoiled. A devotee travels all over the country, from door to door, preaching, “Be Kṛṣṇa conscious. Be a devotee of Lord Kṛṣṇa. Don’t spoil your life in simply fulfilling your animal propensities. Human life is meant for self-realization, or Kṛṣṇa consciousness.” These are the preachings of a sādhu. He is not satisfied with his own liberation. He always thinks about others. He is the most compassionate personality towards all the fallen souls. (from purport)
Full text and purport More
The Hare Krishna Movement 