A reader writes "I have a question
regarding the Clergy taking an oath of celibacy. When did this come about
and why? I've read that Pope Sylvester had several wives. "
First of all, a definition. Celibacy is complete abstinence from sexual activity - it is a vow taken on by monastics of all traditions, by priests in the Roman Catholic tradition, and since Eastern Orthodox bishops are chosen from the monastics, the Bishops in that tradition. Chastity is a virtue enjoined on all Christians - namely abstinence from sexual activity outside of marriage. (This definition obviously is problematic for homosexuals who cannot marry, and also for those for whom marriage's status with the state would cause financial problems. The homosexuality debate is outside the scope of this posting. I have given some personal observations about sexuality and marriage in my previous posts Sex Talk and Sex and Marriage. My position is that while sexuality is important, the church's current obsession with it borders on heresy.)
A good place to start in talking about Clerical Celibacy is with the Apostles of Jesus. We know that Peter was married, and that he traveled with his wife. ((Mat 8:14; Mar 1:30; Luke 4:38, 1Co 9:5) There are some indications that James the brother of Jesus was married, and we know of a husband and wife team of evangelists, Prisca and Aquila (Acts 18.) Others we don't know about, although Paul seems to indicate that they had the "Right" to marry. (1 Cor 9:5)
Vows of celibacy were not unknown in Judaism, but they were rare. Even the withdrawn Essenes allowed their brothers conjugal visits once a year. We have no real indication from tradition that Jesus was involved in a sexual relationship, the Da Vinci Code notwithstanding, but Rabbis were generally expected to marry, in order to carry out the commandment to be fruitful and multiply. Single rabbis today are often under intense pressure to marry.
Greek cults of the time often had virgins or priests that were chaste or even celibate, but it was usually for a period of time rather than permanent.
In the time of Paul, most Christians believed that Jesus was coming back very soon (within their lifetimes) so Paul believed that the married should stay married and the single stay single, so as not to distract from the preparations for Jesus' return. (1 Cor. 7:7-8, "I would that all men were even as myself- but every one has his proper gift from God; one after this manner, and another after that. But I say to the unmarried and the widows. It is good for them if they so continue, even as I.") This does not indicate that Paul was hostile to marriage, simply that he believed that there were more important things considering the time frame.
As monasticism began to rise more and more priests came from that background and kept their vows of celibacy afterward. A major contributor towards the rise of clerical celibacy was the concern over inheritances in Roman Law. Since occupations and property were passed from father to son, a number of difficulties began to arise after the time of Constantine. Priests attempted to pass on church orders and property to their sons in the same way, causing confusion, dissension and lawsuits in the church.
Clerical Celibacy, which was already accepted by monastic priests, was seen as a solution, and as early as 302, the Western church began to call for celibacy, but it was not universally accepted throughout the church until at least 1102 AD.
It is important to note that priestly celibacy has never been a matter of doctrine, or what is believed about the priesthood, but a matter of discipline, or how it is administered, although there does appear to be some movement in the Vatican away from this position.
In the Roman Catholic Church, a matter of discipline can be changed by a decision of a church council or Pope - so the issue is not closed. In fact, some married protestant ministers have been accepted into the Roman Catholic priesthood while not having to renounce their wives, much to the consternation of many celibate Roman Catholic priests.
Martin Luther rejected the idea of clerical celibacy, and all the protestant churches followed suite, although both Anglicans and Lutherans have monastic orders that do take such vows voluntarily.