How do Catholic proponents of priestly celibacy interpret Peter having a wife?
This poses no problems for the Church.
The Church has always maintained that St. Peter was married.
Celibacy is not essential to the priesthood. In fact the Prince of the Apostles, St. Peter was married and traditionally had at least one daughter, St. Petronilla. Her feast day is celebrated at the Vatican on May 31.
Priests of Catholic Eastern Rites and priests of the Eastern Orthodox Churches permit priests to be married. Bishops are universally taken from the ranks of the celibate clergy.
Anglican priests who convert and are married may become Catholic priests without putting their wives aside. They may, by indult, be ordained to the Catholic priesthood while still being married.
Although priestly celibacy is a discipline in within the Latin Rite, priestly celibacy is to be highly praised as a way of imitating the way Our Savior lived himself.
In the early Church, clerical celibacy was not mandated. St. Paul in his first letter to St. Timothy wrote, “A bishop must be irreproachable, married only once, of even temper, self-controlled, modest, and hospitable” (3:2) and “Deacons may be married but once and must be good managers of their children and their households” (3:12). However, one should not erroneously construe this teaching to mean that a bishop, priest, or deacon had to be married; St. Paul admitted that he himself was not married (I Corinthians 7:8).
Furthermore, in over-stressing celibacy as a discipline, it soon becomes a "mere discipline", and a mere discipline is only one step removed from a dispensable discipline. Therefore, discussions which begin by always emphasizing the disciplinary nature of celibacy do so from a prejudiced starting point.
What, then, is a balanced way of approaching this subject? We mentioned above that every discipline exists for the purpose of bearing witness to, buttressing, or exemplifying some teaching of the Faith. Any discussion of the discipline of celibacy must be balanced by a reference to the more fundamental Catholic teaching the practice exists to safeguard.
And what teaching is that? The fact that many of us do not know shows how much we have lost sight of the purpose of this discipline. Too often, attempts to defend celibacy devolve down to three arguments - that it is not practical for a priest to have a family, and that Christ Himself was not married, and that there is a strong tradition of celibacy in the Latin rite. In Benedict XVI's 2007 post-synodal exhortation Sacramentum Caritatis, Benedict links the discipline of celibacy to the fact of Christ's own virginity:
"The fact that Christ himself, the eternal priest, lived his mission even to the sacrifice of the Cross in the state of virginity constitutes the sure point of reference for understanding the meaning of the tradition of the Latin Church. It is not sufficient to understand priestly celibacy in purely functional terms. Celibacy is really a special way of conforming oneself to Christ's own way of life. This choice has first and foremost a nuptial meaning; it is a profound identification with the heart of Christ the Bridegroom who gives his life for his Bride. (Sacramentum Caritatis, 24).
Benedict's statement that Christ's own virginity must be the fundamental point of reference for understanding the tradition is true if we are looking at it from the standpoint of celibacy as an ascetical practice - a manner of living in imitatio christi that signifies the priest's nuptial union to the Church. However, this is not the rationale the early Church used when discussing the discipline; in fact, Benedict's assertion - that Christ's virginity is the point of reference for clerical celibacy - does not appear a single time in any patristic source. There is simply no Church Father or synod that argues that priests should be celibate because Christ was. - The Truth About Priestly Continence and Celibacy in the Early Church
We see the exhortation of St. Paul concerning the office of bishops, in 1 Timothy 3: 1-3:
The saying is sure: whoever aspires to the office of bishop desires a noble task. Now a bishop must be above reproach, married only once, temperate, sensible, respectable, hospitable, an apt teacher, not a drunkard, not violent but gentle, not quarrelsome, and not a lover of money.
For St. Paul being married to a woman for the first time seems to be a prerequisite for the office of the episcopate. Widowers who were remarried would be discouraged from becoming a bishop. Thus the phrase "the husband of one wife” implies that the candidate for this office has never remarried and is either a unmarried widower or married with his first and only wife.
The faithful in the general population have always been free to remarry after the death of their spouses.
1 It is well said, When a man aspires to a bishopric, it is no mean employment that he covets. 2 The man who is to be a bishop, then, must be one with whom no fault can be found; faithful to one wife, sober, discreet, modest, well behaved, hospitable, experienced in teaching, 3 no lover of wine or of brawling, courteous, neither quarrelsome nor grasping. 4 He must be one who is a good head to his own family, and keeps his children in order by winning their full respect; 5 if a man has not learned how to manage his own household, will he know how to govern God’s church? 6 He must not be a new convert, or he may be carried away by vanity, and incur Satan’s doom. 7 He must bear a good character, too, in the world’s eyes; or he may fall into disrepute, and become a prey to the False Accuser. - 1 Timothy 3:1-7
The exhortation of St. Paul in 1 Timothy 3: 1-3 has other interpretations!
The Catholic Encyclopedia infers a rather different approach to this question as follows:
Turning now to the historical development of the present law of celibacy, we must necessarily begin with St. Paul's direction (1 Timothy 3:2, 12, and Titus 1:6) that a bishop or a deacon should be "the husband of one wife". These passages seem fatal to any contention that celibacy was made obligatory upon the clergy from the beginning, but on the other hand, the Apostle's desire that other men might be as himself (1 Corinthians 7:7-8), already quoted) precludes the inference that he wished all ministers of the Gospel to be married. The words beyond doubt mean that the fitting candidate was a man, who, amongst other qualities which St. Paul enunciates as likely to make his authority respected, possessed also such stability of divorce, by remaining faithful to one wife. The direction is therefore restrictive, no injunctive; it excludes men who have married more than once, but it does not impose marriage as a necessary condition. This freedom of choice seems to have lasted during the whole of what we may call, with Vacandard, the first period of the Church's legislation, i.e. down to about the time of Constantine and the Council of Nicaea.
When did the Catholic Church first prohibit bishops from remarrying?
Possibly in 314, we see the first inklings of the notion that the clergy should not remarry after their ordination. What is written for priests and deacons, should apply to higher clergy also.
This is again what we learn from the Council of Ancyra in Galatia, in 314 (canon x), and of Neo-Caesarea in Cappadocia, in 315 (canon i). The latter canon absolutely forbids a priest to contract a new marriage under the pain of deposition; the former forbids even a deacon to contract marriage, if at the moment of his ordination he made no reservation as to celibacy. Supposing, however, that he protested at the time that a celibate life was above his strength, the decrees of Ancyra allow him to marry subsequently, as having tacitly received the permission of the ordaining bishop. There is nothing here which of itself forbids even a bishop to retain his wife, if he were married before ordination. - Celibacy of the Clergy (Catholic Encyclopaedia)
In 1075, Pope Gregory VII made clerical celibacy a mandatory discipline within the Church.
The last pope to be married and pope at the same time was Pope John XVII (1003).
In 1075 Pope Gregory VII issued a decree effectively barring married priests from ministry, a discipline formalized by the First Lateran Council in 1123. Since then celibacy has been required of Roman Catholic priests, though the Catholic churches of the East have continued to allow priests to marry before their ordination. - Why are priests celibate?
Thus, if Pope Gregory VII barred priests from being married, it stands to reason that the higher clergy must also be celibate, bishops and popes included.
Widowers have always been permitted to become priests and bishops.
For further information the following articles may be of interest:
Celibacy is not a dogma but only a disciplinary norm. Why does the Church still attach such great importance to it?
Priestly Celibacy: Apostolic Tradition, not a ‘Mere Discipline’
The Case for Clerical Celibacy: Its Historical Development and Theological Foundations