The Moderator of the Church of Scotland has admitted the George Square tragedy will test Glasgow's faith.
Rev John Chalmers, in a deeply felt open Christmas letter to the city, warned that there were "no trite answers" to why a careering bin lorry would take six lives and damage 10 others.
But the veteran churchman, who has spoken of how his own belief in God was shaken when his soldier son was horrifically wounded in Afghanistan, said people of faith would "travel for as long as it takes with those who have had the heart so indiscriminately ripped out of their lives".
Mr Chalmers was writing as news came that the condition of the youngest victim, a 14-year-old girl, was improving. She and another three injured people, women aged 18 and 64, and a 57-year-old man, remain in hospital.
Mr Chalmers said the shockwaves of George Square had "cut him to the core". He told the city: "I know that courage and fortitude, compassion and sympathy will bring out the very best in you and that in time you will triumph over this disaster, but that is cold comfort today."
But Mr Chalmers added: "It will not be long, however, before real people will be asking why this kind of thing should, in a moment, change the course of the lives of innocent people.
"And those who offer trite answers to that question will, in my view, contribute nothing to the long term care and support required by those whose lives are now changed forever.
"I cannot offer any satisfactory explanations which describe why these things happen; all I can do is offer an assurance that, in deep friendship and out of a conviction that God is on the side of the distressed, women and men of faith will travel for as long as it takes with those who have had the heart so indiscriminately ripped out of their lives."
Clerics of all faiths have been leading prayers and offering comfort this week. Mr Chalmers cited one minister who is sitting with a family which lost a daughter in the tragedy. "She is not trying to offer explanations," he said of the minister, "but her job this Christmas is to be there, to pray with few words and to light a candle in the darkness."
Mr Chalmers - like many others for whom the George Square crash brought back memories of loss - is speaking from experience.
His teacher son, John James - or JJ - Chalmers, a Royal Marine reservist with 42 Commando, survived an IED explosion that killed two of his comrades. The May 2011 blast, however, wounded JJ's face, his arm and his leg.
Mr Chalmers, in his letter to Glasgow, wrote: "Personally, I have been taken to the edge of faith in circumstances where family and friends have been maimed and killed.
"I have been to that place where there was no answer to the question 'Why?'
"I have been ready to throw in the towel on belief, but it was the community of faith that brought me out of the other end of the darkness into a place of greater light. I became stronger for it, and also more understanding."
On Saturday, the Catholic Archbishop of Glasgow told a memorial mass that he wept with a woman who saw her teenage daughter and both her parents die almost right in front of her in the lorry crash.
Jacqueline McQuade is thought to have gone to withdraw money from a cash machine during a Christmas shopping trip when her 18-year-old daughter Erin McQuade and parents Jack and Lorraine Sweeney, all from Dumbarton, were fatally injured.
Archbishop Philip Tartaglia told a 600-strong congregation at the city's St Andrew's Cathedral: "On the evening of the tragedy, I was privileged to be permitted to spend some time with one of the families who had been cruelly devastated by the incident.
"I was able to witness and share the grief and sadness of a mother and of a father for their daughter, and of two daughters for their mother and father.
"The distressed woman to whom I was speaking had been at the incident, she had seen her daughter and her own parents killed almost right in front of her. Can you imagine the horror? Can you imagine her sadness?
"I tried to console them and comfort them. We spoke and we cried and we were silent before the abyss of their loss and the random meaninglessness of what had happened."
Archbishop Tartaglia said the city had been transformed from one "eagerly and cheerfully preparing for Christmas into a city of sadness and mourning".
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