Dr Rowan Williams will invite people to "join the human race" this Christmas and become agents of transformation and renewal.
"Faith begins in the moment of stopping … the moment when you can't just walk on as you did before," he says in his last Christmas sermon as Archbishop of Canterbury.
Dr Williams says that the recent defeat of legislation to allow women bishops has damaged the credibility of the Church.
However, he refuses to be downbeat about the recent Census figures which showed a fall in the number of people calling themselves Christian from 72% in 2001 to 59% in 2011.
Christians should not lose heart, he continues, because faith has to mean more than "what public opinion decides".
"We are after all, doing something rather outrageous, asking men and women to stop and look and turn around, and learn how to keep company with a figure whose outlines we often see only dimly," he says.
The challenge of the Gospel message, he says, is not about religious defensiveness but about the possibilities of transformation.
"Jesus does not come just to answer the questions we think important.
"He does not come to give us a set of techniques for keeping God happy, and he certainly doesn't come to create a harmlessly eccentric hobby for speculative minds.
"He comes to make humanity itself new, to create fresh possibilities for being at peace with God."
The Archbishop shares how, over his decade in office, he has been inspired by people working for peace.
"When people respond to outrageous cruelty and violence with a hard-won readiness to understand and be reconciled, few if any can bring themselves to say that all this is an illusion," he says.
"The parents who have lost a child to gang violence, the wife who has seen her husband killed in front of her by an anti-Christian mob in India, the woman who has struggled for years to comprehend and accept the rape and murder of her sister, the Israeli and Palestinian friends who have been brought together by the fact that they have lost family members in the conflict and injustice that still racks the Holy Land – all these are specific people I have had the privilege of meeting as Archbishop over these ten years; and in their willingness to explore the new humanity of forgiveness and rebuilding relations, without for a moment making light of their own or other people's nightmare suffering, or trying to explain it away, these are the ones who make us see, who oblige us to turn aside and look, as if at a bush burning but not consumed."
The challenge is for everyone, he says, to "join the rest of the human race and acknowledge who you are".
"That's the truest heroism and the hardest," he says.
"It's a foreshadowing of the New Testament invitation: repent and believe and be baptised. Turn round and look where you've never looked before, trust the one who is calling you and drop under the water of his overflowing compassion.
"Be with him. Join the new human race, re-created in the Spirit of mutual love and delight and service."