Reading ancient Christian history through Latter-day Saint eyes, it seems reasonable to assume that ordinations to the Aaronic Priesthood were more common than were Melchizedek Priesthood ordinations. After all, callings in the lesser priesthood typically precede those in the higher, and, just as today, some, for whatever reason, would’ve failed to proceed all the way to the higher priesthood. Moreover, there is reason to believe that entrance into the Melchizedek Priesthood was more restricted anciently than today.
Thus, as legitimate priesthood authority began to disappear from the early church, it would again seem reasonable to assume, on the basis of sheer numbers, that Aaronic Priesthood officers and ordinances lingered longer, and were more prominent, than those of the Melchizedek.
In this light, it’s not surprising that titles and rituals associated by Mormons with the Aaronic Priesthood characterize the ancient churches of Christendom in the centuries following the death of the apostles. Thus, for example, the three major orders of offices in the Roman Catholic, Anglican/Episcopalian, Eastern Orthodox and Oriental Orthodox churches are the diaconate (that of the deacons), the presbyterium (the word literally refers to “elders,” but these are actually priests) and the episcopate (the order of bishops). In The Church of Jesus Christ of Latter-day Saints, deacons and priests are officers within the lesser or Aaronic Priesthood. But so, too, are bishops. Although the office is typically held by a high priest of the Melchizedek Priesthood, it’s actually an Aaronic Priesthood calling, and bishops preside over the Aaronic Priesthood within their wards.
The central ritual of the ancient Christian churches is communion, or the mass. Celebrated by priests, often with the assistance of deacons, it plainly corresponds to the “sacrament” in the LDS Church, the centerpiece of weekly Mormon worship services, which is generally blessed by Aaronic priests and passed to the congregation by deacons. (In the Roman Catholic Church, the term “sacraments” refers to seven acts: baptism, confirmation, the eucharist or communion, penance or reconciliation, the anointing of the sick, ordination to holy orders and matrimony. “Sacrament,” in this sense, approximates what Latter-day Saints mean by “ordinance.”)
Admission to the ancient churches is granted by means of baptism. Similarly, in the LDS Church, baptism is the entry gate into the kingdom. In both, it can be and often is performed by priests.
The removal of the ancient apostles left the far-flung local congregations of the still-young Christian movement isolated under the purely local leadership of presiding elders or bishops. Left to their own devices, lacking a churchwide leadership structure with general authority, these usually good and sincere men did the best they could. Bishops of prominent cities, such as St. Ignatius of Antioch, St. Polycarp of Smyrna and St. Irenaeus of Lyon, wrote treatises and letters attempting to preserve the purity of the faith, as they understood it, against heresies and schisms. St. Ignatius, in particular, stressed remaining in fellowship with one’s bishop as the surest guide to preserving orthodoxy. Eventually, some bishops began to adopt special titles, such as “archbishop,” “patriarch” and “pope” (from the Greek “pappas” and the Latin “papa,” both meaning “father”), and to claim authority over other regional bishops or eventually, in the case of the bishop of Rome, over bishops and Christians everywhere. The title of “pope” seems to have been first applied in the third century to the bishop of Alexandria, Heraclas (d. A.D. 248).
Lacking a quorum of apostles with general authority over the church, how were these bishops chosen? The method has varied over time and from place to place. For centuries, the bishop of Rome, like most other bishops, was chosen by consensus of the ordained clergy and the lay members of the church within the city. In A.D. 1059, however, the body of eligible electors was restricted to the College of Cardinals.
Who were these cardinals? Are they equivalent to the 12 apostles of the original church of Christ? As early as the ninth century, the term “cardinal” (from the Latin “cardo,” or “hinge,” meaning something of literally pivotal importance) was applied to the most prominent priests of the city of Rome. In the 12th century, the practice began of appointing priests from outside the city as cardinals, though each them was — and, most often, still is — assigned a church in Rome as his nominal or titular responsibility. In other words, the pope is a bishop who is elected by a quorum of “local” priests.
Daniel Peterson, BYU professor of Islamic studies and Arabic, founded the Middle Eastern Texts Initiative and MormonScholarsTestify.org, chairs "Interpreter: A Journal of Mormon Scripture," and blogs daily at Patheos.com. The views here are his own.