The bishop said the church must be a church of public truth
The Bishop of Exeter has challenged people to live out their dreams for Christmas 2009 and into 2010.
The Right Reverend Michael Langrish said goals such as peace in the Middle East and ending poverty should not be "just a dream".
He said although people dreamt, "in our hearts we don't think it will happen".
But he said he was daring to dream "because with God anything is possible and the Christmas story teaches us that 'God into man does go'."
In his Christmas message, the bishop said: "We don't let the dream truly take hold of our own actions and attitudes and when that happens to others too, the blockades to the fulfilment of dreams remain very firmly in the way."
He said to his congregation at Exeter Cathedral on Christmas morning he believed this was the problem in the recent climate change talks in Copenhagen.
He said: "If the church is to be the church of Jesus Christ, it must be a church of public truth and public engagement and public action for the long-term good of all, based on the conviction, the eternal dream that 'God is with us'.
"He is with us in Devon and in Darfur, in Afghanistan and with those who suffer Aids, among those homeless and the hopeless, in broken hearts, and broken relationships and broken lives - God into man does go in Jesus, our Emmanuel."