Pope Benedict XVI stepped up his appeals to Orthodox Christians on Wednesday, saying a unified church could help a world ``full of skepticism and doubts'' to believe.  Benedict acknowledged key differences but stressed areas of agreement during a Mass attended by a delegation from the spiritual leader of the world's 200 million Orthodox, Ecumenical Patriarch Bartholomew I. Benedict has made improving relations with Christians, and healing the 1,000-year-old rift with the Orthodox, a ``fundamental'' priority of his papacy. 
  After centuries of moving apart, the churches formally split in 1054 over several issues, including the primacy of the pope, devotional differences, and Latin demands for priestly celibacy, while the Greek-influenced tradition permitted married clergy. Relations remain tense over Orthodox charges of proselytism and rival property claims in places such as Russia and eastern Europe. 
  In his homily, Benedict stressed the unity and universality of the church, but acknowledged key differences over the clout of the pope. The Orthodox see equal distribution of power among their churches, although Bartholomew is considered ``first among equals.''