Yes, priestly celibacy is an apostolic tradition. It is not simply Church law or a human tradition that can be changed; it is apostolic. The Church, particularly the Roman Church, has insisted on it since the earliest centuries, and we have many documents supporting this. Our Lord Himself was celibate, and as the high priest the only high priest His example makes celibacy fitting and more convenient for those who participate sacramentally in His priesthood, namely the priests and bishops.
This celibate life is rooted in the essence of the priesthood. Many of the apostles were married, though not all, but they left everything behind. As St. Peter explicitly said, "We have left houses, children, and wives." Our Lord also said, "Whoever follows Me and leaves behind children, wife, and so on, will receive a great reward." This practice of celibacy was already observed in the third or fourth centuries, as reflected in continuous documents from the Church Fathers, stating that the law of celibacy is of apostolic tradition and is very ancient.
In the first millennium, the law of celibacy was not practiced exactly as it is today in the second millennium. Why? Because in the first millennium, married men could be ordained to the priesthood. However, from the moment of ordination, they were required to live in perfect continence, meaning they could no longer live as husband and wife with their wives. This was a requirement of the Church.
Though this rule was traditional, it was not always perfectly observed, and there were many abuses in the first millennium. Still, it remained the traditional rule. Even today, in the Eastern Churches, some version of this tradition is still maintained. While Eastern Orthodox Churches have married clergy, they do not observe the exact apostolic law of celibacy. In the Orthodox tradition, a married priest who becomes a widower must remain celibate for the rest of his life, even if he had only lived with his wife for a short time before her death.
The law in the Eastern Churches is that a priest must not engage in conjugal relations with his wife on the night before celebrating Holy Mass. He must at least observe one night of celibacy before celebrating Mass. A priest is always a priest, day and night. Catholic priests are encouraged to celebrate Mass daily, and it is considered ideal for every Catholic priest to do so. Therefore, when a Catholic priest celebrates daily Mass, he must always be in celibacy. This is evident from the facts.
Unfortunately, the Eastern Greek Church, especially by the seventh century, formally abandoned this apostolic law and allowed priests to continue their conjugal life after ordination, with the exception of bishops. Only bishops were not allowed to continue living with their wives after ordination. In this way, the Eastern Churches deviated from the exact observance of the apostolic tradition of priestly celibacy and perfect continence.
