Consecrated Life (OSV Encyc. 1997)
The first centuries of Christianity were marked by an awareness that to be a follower of Christ was in itself a call to holiness. Each Christian, baptized in the name of the Father and the Son and the Holy Spirit, felt summoned to dedicate - consecrate - his or her life totally to loving God "with all one's heart and soul and mind" (cf Mt 22:37). The early Christians felt no call to abandon the world, but rather saw it as the place of their vocation and sanctification.
After the passage of some centuries however, this sense that holiness is possible to everyone and that everyone is called to holiness (which the Second Vatican Council has wished to restore: LG, Ch. V) seemed gradually to be lost. Fewer sensed a true call to holiness, and there also grew up a feeling that holiness could be more effectively achieved by separating oneself from the world.
The first expression of this were the hermits, who lived their lives in solitary prayer and penance. Then came the monastic movement, men or women also separated from the world but living together according to a common rule. After that came the mendicant orders and different religious congregations or societies. These tended to become more involved in evangelization and in the direct service of others in society - in schools, hospitals, orphanages, etc. - but still normally as persons "separated" from the world.
This separation from the world is particularly shown in religious life by the profession of the three vows of poverty, chastity and obedience, and by the wearing of a distinctive habit. The habit gives public witness to the fact that God is worth a total dedication of one's life, and that the only thing that really matters is to spend one's self in his service and that of others.