Pope Benedict stunned the Roman Catholic Church including his closest advisers on Monday when he announced he would stand down in the first papal abdication in 700 years, saying he no longer had the mental and physical strength to run the Church through a period of major crisis. Church officials tried to relay a climate of calm confidence in the running of a 2,000-year-old institution but the decision could lead to one of the most uncertain and unstable periods in centuries for a Church besieged by scandal and defections. Several popes in the past, including Benedict's predecessor John Paul, refrained from stepping down even when severely ill, precisely because of the confusion and division that could be caused by having an "ex-pope" and a reigning pope living at the same time. This could create a particularly difficult problem if the next pope is a progressive…