Desert Fathers and Mothers. But the reason goes deeper than just this historical one-off.
You see, one of the reasons that I became a Catholic was because of monks and nuns who have given up everything to follow Christ and God and still do so to this day. I admit that I used to think folks who did this were nuts. But a close reading of scriptures show that it isn't.
Recently, I found a book written by a Paulist Father named Bertrand Louis Conway that helps explain the reasons why this practice isn't strange, but very Christian. Fr. Conway called his book Studies in Church History and he wrote it in response to questions from non-Catholics that came up all the time while he was conducting missions in the Paulist's missionary field. In case you didn't know, that field is here in the United States only.
The excerpt below is from the first chapter of the book. This will get you started,
from Studies in Church History
Christian Asceticism in the First Three Centuries
It is true that the ascetic teaching of Jesus does not hold the predominant place in the Gospels which our rationalistic critics think necessary for our defense of monasticism. But Our Lord did not come to establish a community of monks pledged to the highest degree of perfection, but to found a Church for all men. Our Lord's general moral teaching was undoubtedly most sublime. Christians are to be perfect as their Heavenly Father is perfect; they are all called upon to live a life of self-denial, sacrifice, renouncement, and suffering.
His words are: "I came not to send peace but the sword. ... He that taketh not up his cross is not worthy of Me." "He that shall lose his life for My sake shall find it." "If any man come to Me and hate not his father and mother, and wife, and children, and brethren, and sisters, yea, and his own life also, he cannot be My disciple." Self-denial is an essential characteristic of the true follower of Jesus, and in times of persecution, such as He evidently had in mind in the above texts, this self-denial was to be heroic even unto death.
But there are other teachings of our Savior intended only for an elite few. They are in no sense commandments for the multitude, but counsels left to the free choice of those who were to follow Him more intimately in the way of perfection. Protestantism, cursed with the worldly taint of a merely human gospel, has ever ignored Our Lord's teaching on the counsels. That is the chief reason of its bitter hatred of monasticism and the religious life. That is why the liberal Protestants of today do their utmost to trace the origin of asceticism to a pagan philosophy or a pagan religion.
Jesus mentioned the counsel of chastity in the nineteenth chapter of St. Matthew's Gospel. He was restoring marriage to its primitive purity, and prohibiting divorce even in the case of adultery. When, in view of this strict teaching, the disciples declared: "It is not expedient to marry," Jesus took occasion of their remonstrance to set forth clearly the practice of celibacy "for the kingdom of heaven." The prohibition of divorce is a commandment for all Christians;he practice of celibacy is a counsel for the elite few. "He that can take, let him take it."
Some nonCatholic scholars arbitrarily try to show that these last words of Our Lord refer to the indissolubility of marriage, while others think it strange that our Lord should recommend celibacy while extolling marriage. The first theory does violence to the context, while the second sees opposition where in reality none exists. It is unquestionably true that Our Lord's counsel of celibacy marks the beginnings of asceticism, for virginity is its basic and essential element. Asceticism is possible even when the other practices that generally accompany virginity are absent; but without virginity it does not and cannot exist.
Jesus counseled poverty even more explicitly. He said: "Do not possess gold, nor silver, nor money in your purses." "Take nothing for your journey, neither staff, nor scrip, nor bread, nor money." "Sell what you possess and give alms." "Every one that doth not renounce all that he possesseth cannot be My disciple." "If thou wilt be perfect, go sell what thou hast, and give to the poor."
He did not give a command to the rich young man, but clearly made an appeal to his generosity: "If thou wilt be perfect" are His words. Finally, Jesus asked His chosen ones to renounce their own wills, "to deny themselves and to take up their cross.'' Harnack ( a Protestant author) is wrong in declaring that the Catholic Church teaches two different moral codes, one for the multitude, and another for the monk who stands for a higher type of perfection. The difference between them is merely a difference of degree, or rather of means. Both have the same end in view, viz., the love of God and the love of the neighbor for God's sake.
Read the rest, with all the footnotes, at the YIMCatholic Bookshelf.