Swami Dayananda Saraswati
Published in the 5th Anniversary Souvenir of the Arsha Vidya Gurukulam, 1991.
In Sanskrit the word for renunciation is sannyasa and one who is a renunciate is called a sannyāsi. Generally the life of renunciation is associated with a life of austerities, of self-denial, or of monasticism. The Bhagavadgita defines a sannyāsi as (5-3):

The person who neither hates nor longs (for anything) should be known as always a renunciate (sannyāsi), O Arjuna, because one who is free from the opposites (likes and dislikes) is effortlessly released from bondage.
As such, the word sannyāsi means a person who can handle his feelings towards the world; a person, who in spite of the situation is able to maintain equipoise. Another word for a renunciate is sādhu or “a good person”; that is, a person who can be trusted, whose mind causes no one any consternation, a simple person whose life is one of values; of gentleness and of honesty. Being a sādhu really means being a person whose mind is resolved about his life. This person can be from any walk of life – a parent, a businessperson, a monk, etc. One’s attitude to life is the basis of being a sādhu.
In India, the tradition of monasticism is symbolized by orange cloth, and generally a person inclined towards the direction of a monk wears orange. The orange symbolizes the first rays of the sun rising at dawn—the rays which destroy the darkness; that is, the color orange stands for knowledge, the dispeller of ignorance. Orange is also the color of fire symbolizing the burning of the problems that characterize human life. These problems are known as karma—which may be either good or bad and which bind a person to a life of bondage. Thus, the color orange represents jñānam, self-knowledge.
Throughout history there have been those who truly owned up the qualities associated with the cloth and those who did not. In Bhaja Govindam, the author warns us of a person whose behavior is mithyācara, untrue to the nature of the robe he is wearing. “An ascetic with matted locks, one with a shaven head, or one whose hairs are pulled out one by one, or one wearing ochre robes, deluded they are, who though seeing, do not see. Truly these different disguises or clothing are merely for the sake of filling the belly.”
Alternatively, there are people who do not wear the robes, but who have this knowledge and the associated values. A sādhu is someone whose mind is sādhu, who has a sādhu buddhi, who lives his life simply, without personal conflict.
Traditionally, if one chooses the life of a monk, one is absolved from the normal duties in society. In India, a monk who seeks to understand the truth is supported by the community. He is also known as a biksu, a person who lives on alms. Generally there are two lifestyles associated with being a monk: that of a bee, a person who wanders from place to place and who receives his food from different sources; and that of a python, a person who sits in one place and accepts whatever food comes to him.
At the time of receiving this cloth, which is given by one’s teacher, a sādhu is asked to say the abhaya mantra, a vow wherein he promises not to cause injury to any part of the creation whatsoever. His vow is neither to hurt nor to be hurt as he lives in a world where it is so easy to hurt and to be hurt. The understanding that is involved in order to commit oneself to a life of not hurting is really what it takes to be a sādhu.