The Archbishop of Canterbury will speak of how he has been inspired by meeting people who have experienced great suffering, such as victims of gang violence.
Delivering his final Christmas Day sermon from Canterbury Cathedral, Dr Rowan Williams will also acknowledge how the General Synod's vote against allowing women to become bishops last month has damaged the credibility of the Church.
But, he will also point out a reason to be positive, in the recently published census statistics, which indicated that 59% of people still identified themselves as Christian.
Dr Williams, who steps down at the end of the month after a decade as head of the Church of England, will speak of some of the people he has had the "privilege" to meet during his tenure.
"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 will say.
"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."
Referring to the 2011 census, he will say that faith has to mean more than just "what public opinion decides", and Christians should not lose heart.
"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 will tell the congregation.
Dr Williams, who is to take up the posts of Master of Magdalene College Cambridge and chairman of the board of trustees of Christian Aid, is to be replaced by former oil executive the Rt Rev Justin Welby, the Bishop of Durham.