From about the year 400 to about 1970 members of religious orders have played a very important part in the lives of ordinary parishioners, in both the Western and Eastern Churches. In the Middle Ages monasteries and convents dotted the countryside and towns, each exercising a powerful influence on parishioners both nearby and distant.
The early idea of a monk is of a man who lives alone (Greek monos), that is, cut off from the world. These men formed communities governed according to a set of rules. The most common and notable were the Benedictines, with reformed varieties such as Cistercians. But there were many other Orders of monks.
What is our picture of a medieval monastery? Perhaps of a large house and church, surrounded by fields cultivated by monks. Perhaps we see them at times reciting or singing throughout the day and night long liturgical prayers, copying manuscripts, studying, and doing manual work. We need to modify that picture.
Monasteries contained both large and also small numbers of monks. One monastery might have 200 monks, another only 25. In general, most monks were not priests but laymen or clerics in minor orders (e.g., subdeacon). For centuries boys were left by parents to become monks as gifts to a monastery.
This recruitment method was gradually abandoned with entrants spending a year in a novitiate being taught to read so as to be able to recite the offices and do spiritual reading; but most had little book education. Monks took vows of poverty, chastity, obedience and stability, that is, to stay in the one monastery all their lives. Once they took their vows they could never leave. That law applied to all religious orders.
By 1200 monks did little pastoral or missionary work. One can see this in places like Westminster and York where a parish church to serve the people and staffed by secular clergy lies beside a very large church reserved to monks and employees and guests of the monastery. Most monks no longer took part in manual labour being preoccupied with the huge business of the estates of the monastery.
Often a monastery contained conversi, unpaid laymen who followed a rule, semi-monks who performed servant-like roles. On the other hand, paid servants constituted about half of the inhabitants of a monastery with officials like priors having their own servants. In addition there were "retirees", people who had donated land or entitlements to the monastery and acquired a right to live therein. These might have their wives and servants with them.
The lands of an English monastery could be scattered over many counties in Britain and in France, even in Denmark, for example, Fountains Abbey in Yorkshire held lands in 151 places. Usually a small number of monks constituting a "cell" lived on these estates to administer them.
So we see that a monastery was a very large community with widespread influence and that commonly the monk was deeply enmeshed in the world. As a physical entity, there was a central house, comprising dormitories, cellars, kitchens, storage rooms, guest house and brewery, as well as a sometimes large church.
The whole complex, including the abbot's house, would resemble a large village. Abbots were in effect lords of manors who held courts, and governed towns and villages. In England they sat in what was later called the House of Lords and often acted as ambassadors. The abbot usually had a separate house, with its own kitchen, cellar, guest house, chapel, and houses for lay staff.
Many abbots were rarely in the monastery and lived in great style, receiving a handsome pension when they retired. But there was more to a monastery than that. Whole towns and villages and castles belonged to monasteries, along with granges, holiday homes, houses for collection of rents, storage sheds, bakeries, mills, ovens, roads (with rights to charge tolls for their use). Thousands of people were affected by a monastery.
The orders of friars originated about 1200, the main ones being Franciscans, Dominicans, Carmelites, and Augustinians, but over time other small orders of friars developed. The Franciscans grew in numbers at a prodigious rate. There were twelve friars when the order began in 1209 and by 1221 there were more than 3,000; 25,000 in about 1290; and in 1316 some 30,000. They attracted recruits because of their poverty and austerity and close imitation of Christ.
Friars were distinguished by not being tied to one place, so their reach was international and they were directly subject to popes and, in general, loyal to them. They also soon became learned. Dominicans sought intellectual excellence and soon became university teachers, producing famous philosophers and theologians, such as St Thomas Aquinas, Duns Scotus and William of Occam. Friars often settled in towns where their example and preaching proved very influential.
Nuns were not so numerous in the Middle Ages because they were aristocratic and enclosed. In England they usually spoke French, the language of the aristocracy. Each candidate had to bring a substantial dowry to the convent (monastery). Their main task was to pray the Divine Office, and to intercede for the dead, who often had donated the estate for the convent. Reading was important, so they were literate.
So we see that while medieval Church institutions resembled those of today in some respects, because of the historical context, they differed markedly in others.