Renunciation and monasteries (ashrams) play an extremely important part in Hinduism. The monks (sanyasis) and nuns (sanyasinis) are among the most important sustainers and propagators of the Dharma. One of the basic teachings of Sanatana Dharma is that all suffering is caused by craving for sense‐gratification (consumerism) and attachment to material possessions, people and circumstances. It therefore follows that renunciation of the material world and consumerism will lead to happiness, and the doctrine of renunciation (sanyasa) is one of the pillars of Sanatana Dharma. This renunciation must be a total mental act in order to be effective, physical renunciation without the mental conviction is a waste of time!
The monastics are all those men and women who have renounced the world and all formal religious expression. This means that they no longer perform rituals on behalf of themselves or others and restrict their practices to meditation and study of the Upanishads which deal with theological and philosophical matters, and the teaching of Dharma. They may be ex‐priests but mostly they are lay people from all four castes who have taken to this calling. Some reside in monastic centers (ashrams or mathams) and some live alone and make their living by begging.
When one becomes disenchanted with material life, and decides to renounce everything one goes off and take up residence in a monastery (ashram). There, after leading the life of a celibate neophyte for seven to twelve years one may take the final vows of a monk/nun and don the saffron robe. These vows are irrevocable and taken only after great deliberation. The life of a monk/nun is one of dedication to the spiritual path and the pursuit of enlightenment. All their actions are dedicated to the welfare of all beings.
There is no central ecumenical authority or hierarchy and even the sectarian orders that do exist are more democratic and independent than authoritarian and structured. Most initiated orthodox Hindu priests owe allegiance to a monastic seat (Matham or Pitha) and the pontiff of such a Matham is consulted in matters of religious law and protocol but has no authority over the priests.