Pope Francis urged Catholic bishops on Wednesday to dream of a future free of the mistakes and sins of the past, as he opened a global gathering of the church leadership amid renewed outrage over the priestly sex abuse and cover-up scandal.Francis celebrated Mass in St Peter's Square with more than 200 priests, bishops and cardinals summoned to Rome for a monthlong meeting on proposing new ways to minister to today's young Catholics.Francis prayed for the bishops to guide the young with experience, but also rekindle in themselves the gift of "dreaming and hoping" that young people have.He prayed for God's help to ensure that the church "does not allow itself from one generation to the next to be extinguished or crushed by the prophets of doom and misfortune, by our own shortcomings, mistakes and sins".The October 3-28 synod is opening under a fresh cloud of the abuse scandal has seen new revelations about decades of wrongdoing in the US, Chile, Germany and elsewhere. That has sent confidence in Francis' leadership to all-time lows among the American faithful.A survey by the Pew Research Centre released on the eve of the synod found that just 31% of US Catholics felt the pope was doing an excellent or good job in addressing the abuse issue, down from 45% in January and 55% in 2015.Francis didn't refer directly to the scandal in his homily, but he did urge the synod members to "reverse situations of uncertainty, exclusion and violence, to which our young people are exposed".Let us "transform those frames of mind that today paralyse, separate and alienate us from young people, leaving them exposed to stormy seas, orphans without a faith community that should sustain them, orphans devoid of a sense of direction and meaning in life", he said.Francis visibly and audibly choked up during his homily when he welcomed two Chinese bishops to the gathering. Their presence was made possible thanks to a landmark agreement with Beijing over bishop nominations that unified the Chinese Catholic leadership for the first time in decades."Today, for the first time, we have also with us two bishops from mainland China," Francis said, pausing to compose himself. "We offer them our warm welcome."The presence of Bishops Guo Jincai of Gengde and Yang Xiaoting of Yan'an at the synod was of such significance that one of the pope's communications advisers tweeted a selfie with them."The joy and consolation of full communion in the church," tweeted the Rev Antonio Spadaro, editor of the Jesuit journal La Civilta Cattolica.