IN AN interview with a German magazine earlier this month, Pope Francis suggested that he would be open to the idea of allowing married men to become priests. Such a change, though momentous, would be a return to, rather than a break from, early Christian tradition: nowhere does the New Testament explicitly require priests to be celibate. For the first thousand years of Christianity it was not uncommon for priests to have families. The first pope, St Peter, was a married man; many early popes had children. How did celibacy become part of the Catholic tradition?

Celibacy is one of the biggest acts of self-sacrifice a Catholic priest is called upon to make, forgoing spouse, progeny and sexual fulfilment for his relationship with parishioners and God. According to the Catholic Church’s Code of Canon Law celibacy is a “special gift of God” which allows practitioners to follow more closely the example of Christ, who was chaste. Another reason is that when a priest enters into service to God, the church becomes his highest calling. If he were to have a family there would be the potential for conflict between his spiritual and familial duties. The Vatican regards it as being easier for unattached men to commit to the church, as they have more time for devotion and fewer distractions.

The earliest written reference to celibacy comes from 305AD at the Spanish Council of Elvira, a local assembly of clergymen who met to discuss matters pertaining to the church. Canon 33 forbids clerics in the church—bishops, priests and deacons—from having sexual relations with their wives and from having children, though not from entering into marriage. It was not until ecumenical meetings of the Catholic Church at the First and Second Lateran councils in 1123 and 1139 that priests were explicitly forbidden from marrying. Eliminating the prospect of marriage had the added benefit of ensuring that children or wives of priests did not make claims on property acquired throughout a priest’s life, which thus could be retained by the church. It took centuries for the practice of celibacy to become widespread, but it eventually became the norm in the Western Catholic church.

Despite the decrees from the Middle Ages, celibacy is still a “discipline” of the church, which can be changed, rather than a “dogma”, or a divinely revealed truth from God which cannot be altered. As the world has changed, the Church has had a harder time recruiting priests. Numbers have been dropping: between 1970 and 2014 the world’s Catholic population grew from 654m to 1.23bn, while the number of priests declined from 420,000 to 414,000.Some prospective priests don’t want to choose between having a life with God and having a family. It is not inconceivable that the time will come again when they can have both.