The murder of a priest at the very altar where he is celebrating Mass – the supreme act of Christian worship - strikes horror in everyone’s hearts. But I think it must be of particular anguish for other priests. For their own priestly lives are dedicated, on altars throughout the world, to re-enacting the sacrifice of Christ at Calvary. The sacrifice of the Mass is unbloody – until, in a rare act of violent theatre, the celebrant is the victim, slain alongside his own altar.

The slaughter of Fr Jaques Hamel, aged 85, by terrorists linked to ISIS, in a quiet suburb of Rouen yesterday, was an act of deliberate outrage against the Christian faith. So many details add to the pathos and sorrow of this barbaric act. Father Hamel could have presented no physical threat to his assailants. Recent photographs show him looking frail and old – but still devoted to his priestly vocation and, although retired, still helping out at the parish where he has been a familiar presence for many years.