Celibacy is the formal and solemn oath to never enter the married state. In the Catholic Church, men who take Holy Orders and become priests and women who become nuns take a vow of celibacy. Celibate men and women willingly relinquish their right to marry in order to devote themselves completely and totally to God and his Church.
Celibacy and the male priesthood are two separate and distinct issues and entities, even though they overlap in practice. Celibacy is a discipline of the Church that isn’t absolute; exceptions and modifications have been made through the centuries. But the male priesthood is a part of doctrine and divine law that can never be changed or altered by any pope or council.
The Catholic Church doesn’t teach (and never taught) that all clergy must be celibate. From day one, Eastern Catholic Churches, such as the Byzantine, have consistently and perennially had the option of married clergy. Only in the United States is celibacy imposed and forced on the Byzantine Catholic clergy. Both the Eastern Catholic and Orthodox Churches maintain that only celibate priests can become bishops.
A man may be ordained when he’s single or married if he’s Eastern Catholic, but after ordination, a single cleric can’t marry, and a married cleric can’t remarry if his wife dies, unless they have small children and he receives a dispensation from Rome. Marriage must precede ordination according to Eastern tradition, or it can never be received.
The reason for a celibate priesthood is partly political. From the fifth to eighth centuries, the most powerful and influential person in the West was the Catholic pope in the absence of a strong ruler in Europe. Kings, princes, barons, earls, dukes, counts, and other nobility married first to make political alliances and second to establish families. Mandatory celibacy prevented the clergy from getting involved in the intrigue of who marries whom. Mandatory celibacy ensured that the priests were preoccupied with Church work and had no ties or interests in local politics among the fighting factions, which were trying to establish the infant nation states.
The Catholic Church uses the Bible as part of its reasoning for priestly celibacy. Jesus Christ never married and was celibate, and passages in Matthew (19:12) and first Corinthians (7:8 and 7:27–34, 38) affirm the value of celibacy.
Mandatory celibacy for the priesthood is a discipline of the Church, not a doctrine or a dogma. Theoretically, any pope could modify or dissolve mandatory celibacy at any time, but it’s highly improbable, because it’s been part of the Western Church’s priesthood since the fourth century. Additionally, the Church teaches and affirms that celibacy isn’t just a sacrifice; it’s also a gift.