Darrell Guder was shocked when Pope Benedict XVI announced on Monday that he will step down from the papacy on Feb. 28.
Benedict XVI is the first pope to resign from office in nearly 600 years. Typically a pope dies rather than retires.
"I would say it was stunning," said Guder, the Henry Winters Luce Professor of Missional and Ecumenical Theology at Princeton Theological Seminary. "Everyone here has had the same reaction. "It's a very, very remarkable step for the pope.
"From what I've read, a very responsible, thoughtful decision that has a very high level of integrity," Guder said.
A pope hasn’t resigned since Pope Gregory XII did so in 1415. The last pope, John Paul II, suffered from Parkinson's disease for years before he died in 2005.
Benedict XVI made a different choice, announcing that he would step down due to his declining health.
"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry," was Benedict XVI's statement in part.
"I am well aware that this ministry, due to its essential spiritual nature, must be carried out not only with words and deeds, but no less with prayer and suffering," he continued. "However, in today’s world, subject to so many rapid changes and shaken by questions of deep relevance for the life of faith, in order to govern the bark of Saint Peter and proclaim the Gospel, both strength of mind and body are necessary, strength which in the last few months, has deteriorated in me to the extent that I have had to recognise my incapacity to adequately fulfil the ministry entrusted to me."
Guder said the question now is whether Benedict XVI will have any influence over the choice of the next pope.
"Based on the motivation of his decision, I think he will continue to be scrupulous and will withhold himself from the decision," Guder said. "And of course, with the potential of (the next pope) being a non-European, I'm hoping the College of Cardinals will be visionary in their choice because of its effect on all of us, Catholic or not."