As The National Catholic Reporter points out, one of the reasons Pope Benedict XVI's resignation is so surprising is because "most modern popes have felt resignation is unacceptable. As Paul VI said, paternity cannot be resigned."
Indeed, as Mark noted earlier, a papal resignation hasn't happened for nearly 600 years.
What's clear is that the code of canon law allows for the resignation of a pope. What we find more interesting, however, is the discussion of theology that Benedict's resignation has sparked.
Take America Magazine, for example. They, of course, look at how different a decision Benedict made compared to John Paul II, who remained pope even as his health slowly declined and he could hardly speak or walk on his own.
"Pope Benedict XVI and Pope John Paul II reached entirely different conclusions to the same question: Should an ailing pope resign? For John Paul, the image of the suffering, sick pope was of spiritual value to his flock; for Benedict, the job needed to be done. Discernment is always very personal; and it is important to see how two holy men reached two entirely different decisions. God speaks differently to different people facing the same question. In the lives of the saints, for example, we often see how the same situation is handled differently by different saints. When St. Francis of Assisi was facing a painful malady of the eyes, brought on, doctors thought, by excessive tears during Mass, St. Francis decided that he would continue as he had with the celebration of Mass. When St. Ignatius faced similar problems with his eyes, the physicians warned him, he decided to curtail his devotions, in order to have sufficient health to do his work. Both were responding to what they felt were God's promptings in their lives."
Brian Flanagan, an assistant professor of theology at Marymount University, believes Benedict's resignation signals a huge shift in how Catholicism views the papacy.
In his view, Benedict's resignation, he writes on his blog Daily Theology, affirms that the power of the papacy lies with the office, not the man. He writes:
"The pope exercises his authority as the bishop of Rome and, because of that, the universal pastor, as the head of a local church, not because of a permanent change in his personal status (like being baptized, being ordained or being made a cardinal). Benedict's own ecclesiological background is helpful here, in that he knows very well what a difference this makes. One could even speculate that this is a not-so-subtle contrast with the personality-driven papacy of his predecessor, John Paul II, a style of papacy that Benedict has studiously avoided. In addition to the possible practical benefits of having a younger man (in Vatican terms...) at the helm, preventing the administrative and bureaucratic mayhem of the last years of John Paul's papacy, this move symbolically brings the papacy down to its proper size. The papacy can now be clearly seen as a crucial office of the universal church, but one in which the pope remains an officeholder, rather than an irreplaceable, magical figure. I'd bet 20, if the Vatican could accept credit cards, that Benedict is doing this with a great deal of conscious awareness of the ecclesiological, and not just the practical, implications for future papacies. The precedent may well be his greatest gift to the church."