Should Christians fight? Should we spread our religion by force? Should we defend ourselves and others using force?
Early Christians were pacifists. Jesus Himself taught to turn the other cheek. He said 'do not resist an evil man' in The Sermon on the Mount. It's the peacemakers who are blessed, not the warmongers. His followers would rather take a beating than give one. They were to be people of pure love.
This didn't last though. As Christianity took the reins of empire, the likes of Augustine of Hippo and Ambrose of Milan authorised the state to employ violence, against both enemies and criminals.
As the great apostasy took over, knights were used to attack enemies and force conversions. They were promised get-out-of-purgatory-free cards and the pope's blessing. Orders of warrior monks were established to fight for 'Christ'. Yes, this same Christ who told Peter in the garden of Gethsemane that 'those who live by the sword, die by the sword'.
Is it ever right to fight? I'd say perhaps. I respect anyone who joins our armed forces serving Queen and country. I speak English and can vote for my government today because previous generations gave their lives and fought the evils of fascism. Nevertheless, many Christians refused conscription to fight in the First World War under the auspices of the 1916 Military Service Act. I would suggest that Christians must not fight for their own gain, but may, conscience permitting, in defence of others and their country.
We must never, however, physically fight for our God and our faith. God can, and will, fight and defeat His enemies in His own time and way. As the Quaker Peace Testimony states: 'we shall not fight for the kingdoms of this world, or the Kingdom of Christ'.
Our crusading friend may have been disappointed to discover that purgatory is not real. And for his use of that sword, he will be held accountable.