Taken from God’s War by Christopher Tyerman

The Christian Problem Of Misinterpretation:

“…The language was especially striking, with its persistent emphasis, not only on St. Peter, as was usual in his calls to arms, but on Christ Himself: ‘the example of our Redeemer and the duty of brotherly love demand of us that we should set out hearts upon the deliverance of our brethren. For as He offered his life for us, so ought we to offer our lives for our brothers.’ Gregory hoped he cold ‘with Christ’s help carry succour to the Christians who are being slaughtered by the pagan’; preferable even to dying for one’s  country, ‘it is most beautiful and glorious indeed to give our mortal bodies for Christ, who is life eternal’. He called on the faithful ‘to defend the Christian faith and serve the heavenly king’ thus ‘by a transitory labour you can win and eternal reward’.”

The Muslim Problem Of Obligation:

Unlike Christian concepts of holy war, to which the Islamic jihad appears to have owed nothing, jihad was fundamental to the Faith, described by some as a sixth pillar of Islam. In theory, fighting was incumbent on all Muslims until the whole world had been subdued, but it was a spiritual as well as military exercise from the start, and a corporate not individual obligation.”