One further word on the canonical legislation of the Middle Ages. On various occasions, in penitential books, it is said that for a married priest to go on having sexual relations with his wife after ordination would be an act of unfaithfulness to the promise made to God. It would be an adulterium since, the minister now being married to the Church, his relationship with his own wife «is like a violation of the marriage bond».28 This weighty accusation against a lawfully wedded, decent man only makes sense if something is left unexpressed because it is well-known, i.e., that the sacred minister, from the moment of his ordination, now lives in another relationship, also of a matrimonial type — that which unites Christ and the Church in which he, the minister, the man (vir), represents Christ the bridegroom; with his own wife (uxor) therefore «the carnal union should from now on be a spiritual one», as St Leo the Great said. 29[...]
In later times, the separation was introduced between priesthood and marriage. And so the formula unius uxoris vir, in its literal and material sense, is no longer of immediate application to the priests of today, since they are not married. Yet paradoxically, precisely in this lies the interest of the formula. We set out from the fact that in the apostolic Church it was only used for clerics; and so it took on, besides the immediate sense of conjugal relations, a further, mystical sense, a direct connection with the spiritual marriage between Christ and the Church. St Paul was already hinting at this. For him, unius uxoris vir was a covenantal formula: it introduced the married minister into the marriage relationship between Christ and the Church; for Paul, the Church was a ‘pure virgin’, it was the ‘bride’ of Christ. But this connection between the minister and Christ, due to the sacrament of ordination, today no longer requires as human support for the symbolism a real marriage on the part of the minister; so the formula is still valid for priests of the Church, although they are not married. Hence, that which in the past was continence for married ministers, in our own day becomes the celibacy of those who are not. Yet the symbolic and spiritual meaning of the expression unius uxoris vir remains ever the same. Indeed, since it contains a direct reference to the covenant, that is to say, to the marriage relationship between Christ and the Church, it invites us to attach much greater importance today than in the past to the fact that the minister of the Church represents Christ the bridegroom to the Church his bride. In this sense, the priest must be «the husband of one wife»; but that one wife, his bride, is the Church who, like Mary, is the bride of Christ.
It is precisely thus that on various occasions John Paul II expresses himself in his post-synodal Apostolic Exhortation Pastores dabo vobis. By way of conclusion, we quote some of the more telling passages from it.
In n. 12, having said that, as regards the identity of the priest, his relationship with the Church must take second place to his relationship with Christ, the Pope goes on: «As a mystery, the Church is essentially related to Jesus Christ. She is his fullness, his body, his spouse... The priest finds the full truth of his identity in being a derivation, a specific participation in and continuation of Christ himself, the one High Priest of the new and eternal covenant; the priest is a living and transparent image of Christ the Priest. The priesthood of Christ, the expression of his absolute ‘newness’ in salvation history, constitutes the one source and essential model of the priesthood shared by all Christians and the priest in particular. Reference to Christ is thus the absolutely necessary key for understanding the reality of priesthood.» On the basis of this very close union between the priest and Christ, the deep theological reason for celibacy is easier to grasp.
With apologies for the long quote. The emphasis is mine.
[from www.tradito.com]
Clerical celibacy has a biblical basis in the evangelical counsel of Our Lord as relayed in St. Matthew's Gospel (19:12), also taken up by St. Paul in his First Epistle to the Corinthians (7:8-9, 25-26, and especially 32-35), and confirmed by St. John in the Apocalypse (14:4-5). It is clear that once the Apostles received the call, they did not lead a married life.
The tradition of clerical celibacy was solemnly proclaimed by the Council of Nicaea, the First Ecumenical Council, in 325. Canon No. 3, unanimously approved by the Fathers, admitted of no exceptions whatsoever. The Council considered that the prohibition imposed thereby on all bishops, priests, and deacons against having a wife absolute. All subsequent councils that have addressed the subject have renewed this interdiction.
Not only would it be a violation of Sacred Tradition to blot out a custom decreed for 2,000 years to be absolutely obligatory, but also one must recognize that clerical celibacy is to be seen not merely as of ecclesiastical institution, but part of what is more broadly known in Catholic moral theology as "divine positive law," initiated by Christ and His Apostles. That is, it is not merely disciplinary in nature.
The Council of Carthage in 390 stated that celibacy of is Apostolic origin.
St. Epiphanius of Salamis (ca. 315-403): "It is the Apostles themselves who decreed this law."
St. Jerome (ca. 342-420): "Priests and deacons must be either virgins or widowers before being ordained, or at least observe perpetual continence after their ordination.... If married men find this difficult to endure, they should not turn against me, but rather against Holy Writ and the entire ecclesiastical order."
Pope St. Innocent I (401-417): "This is not a matter of imposing upon the clergy new and arbitrary obligations, but rather of reminding them of those which the tradition of the Apostles and the Fathers has transmitted to us."
St. Peter Damian (1007-1072) wrote: "No one can be ignorant of the fact that all the Fathers of the Catholic Church unanimously imposed the inviolable rule of continence on clerics in major orders."
There is a reason for this Tradition. The cleric in major orders, by virtue of his ordination, contracts a marriage with the Church, and he cannot be a bigamist. St. Jerome in his treatise "Adversus Jovinianum," bases clerical celibacy on the virginity of Christ.
The universal law of clerical celibacy confirmed by the Council of Nicaea applied, and still applies, to the Eastern Church as well as the Western. It is noteworthy that at that Council, the Easterns (Greeks) made up the overwhelming majority. Previously, the Council of Neo-Caesarea (314) had reminded all Eastern clerics in major orders of the inviolability of this law under pain of deposition.
The Eastern Church began at a late date to violate its own law of celibacy. The Quinisext Council of 692, which St. Bede the Venerable (673-735) called "a reprobate synod," breached the Apostolic Tradition concerning the celibacy of clerics by declaring that "all clerics except bishops may continue in wedlock." The popes refused to endorse the conclusions of the Council in the mater of celibacy, and the Eastern Church planted the seeds of its schism.
The German scholar, Stefan Heid, in his book, Celibacy in the Early Church, demonstrates that continence-celibacy after ordination to the priesthood was the absolute norm from the start -- even for the separated married ordinand -- a triumph of grace over nature, so to speak. The Eastern practice we now see was a mitigation of the rule, not, as the Modernists like to claim, the original practice from which the Roman Catholic Church diverged.