Question: Why are Orthodox clergy allowed to marry and some other clergy are not?
Answer: Many sources exist to help give you an answer to this question. One that generally sums up the various details and is easily accessible is excerpted below, from Wikipedia.com (check out the following website - http://en.wikipedia.org/wiki/Clerical_celibacy - for more details).
In some Christian churches, priests and bishops must remain unmarried, while in others, married men may be ordained as deacons or priests, but may not remarry if their wife dies. Since celibacy (renouncing marriage) is seen as a consequence of the obligation of continence (refraining from any form of sexual intercourse), it implies abstinence from sexual or romantic relationships. In the case of the Latin (Roman Catholic) Church, the specific obligation of the clergy is continence. The Code of Canon Law prescribes that, “Clerics are to behave with due prudence towards persons whose company can endanger their obligation to observe continence or give rise to scandal among the faithful.”
In some Christian churches, a vow of chastity is made by members of religious orders or monastic communities, along with vows of poverty and obedience, in order to imitate the life of Jesus of Nazareth. This vow of chastity, made by people not all of whom are clergy, is different from what is the obligation, not a vow, of clerical continence and celibacy. Celibacy not only for religious and monastics (brothers/monks and sisters/nuns) but also for bishops is upheld by both the Roman Catholic Church and Orthodox Christian traditions.
In Latin Rite Catholicism, all priests must be celibate men, unless given special permission; but in most Orthodox traditions and in some Eastern Catholic Churches men who are already married may be ordained priests, but priests may not marry, whether for the first or second time, while bishops must be unmarried men or widowers. Neither the Catholic nor the Orthodox tradition consider the rule of clerical celibacy to be a dogma, but instead as a rule that could be adjusted if thought appropriate. However, the likelihood of this rule changing in our lifetime is very, very small.
Historically, arguments both for and against married clergy existed from early centuries. Both the New Testament and early Christian writings indicate that some Apostles and bishops were married. By the fourth century, if bishops were married before they were elevated, they and their wives were expected to be continent (see definition above). The earliest known official prohibition to sexual relations - even with one’s spouse - is that of the western Council of Elvira (c. 306): “Bishops, presbyters, deacons, and others with a position in the ministry are to abstain completely from sexual intercourse with their wives and from the procreation of children. If anyone disobeys, he shall be removed from the clerical office.”
By the 12th century, the Second Lateran Council (1139) made celibacy mandatory for all clerics (deacons, priests, and bishops) of the Roman Catholic church. By the 16th century, the Reformers made abolition of clerical continence and celibacy a key element in their reform. They denounced it as opposed to the New Testament recommendation that a cleric should be "the husband of one wife" (see on 1 Timothy 3:2-4 above), the declared right of the apostles to take around with them a believing Christian as a wife (1 Corinthians 9:5) and the admonition, "Marriage should be honoured by all" (Hebrews 13:4). They blamed it for widespread sexual misconduct among the clergy.
Orthodox Christian tradition still holds that a bishop must be celibate and continent, but that a married man may be ordained a deacon or priest provided he is married before ordination. However, whether married or celibate, all clergy, regardless of denomination, have a responsibility first to God and then to their families and congregations to live a life that glorifies Christ and that to the best of their abilities, keeps them prudent in their relationship with others so as not to “give rise to scandal among the faithful.”