In his book Dei gesta per Francos or "God's deeds through the Franks", Guibert of Nogent uses biblical exegesis to justify the Crusades as well as to legitimize the actions of the First Crusade. For the men of the eleventh century and more importantly Guibert, this entire endeavour was merely the crowning of an alliance between God and the Franks, and after the discourse of Urban II at Claremont, it was to the cry of "God wills it!" that all made haste to take Jerusalem back from the hands of the infidels. Throughout Dei gesta, Guibert uses tropological readings of actions in the Bible to provide a sense of morality to the First Crusade.
People of the Middle Ages did not separate themselves from classical people in thought or deed; rather, they saw themselves in continuity with the ancient world, in particular the actions of people in both the Old and New Testament. Guibert uses allegory as a synthesizing agent to bring together a whole image linking the Crusaders to characters in the Bible. Throughout the book Guibert relentlessly insists that the Crusaders outdo the ancient Jews; indeed in the last part he attempts to strip them of every accomplishment:
"The Lord saves the tents of Judah in the beginning, since He, after having accomplished miracles for our fathers, also granted glory to our own times, so that modern men seem to have undergone pain and suffering greater than that of the Jews of old, who, in the company of their wives and sons, and with full bellies, were led by angels who made themselves visible to them."
By mentioning and equating actions of the Jews in the Old Testament to the actions of Crusaders Guibert provides not only a sense of attachment but a sort of superior moral high ground as Crusaders appear to have endured more for the sake of their cause and had more faith then that of their spiritual predecessors. Guibert does not let up on the superiority of the current generation over previous ones saying, "Let us look carefully, indeed let us come to our senses about the remains, I might have said dregs, of this time which we disdain, and we may find, as that foolish king said, that our little finger is greater than the backs of our fathers, whom we praise excessively".
Throughout chapter four, Guibert references both the New Testament equating the actions of the people there to actions that Crusaders took and should perhaps continue in the future. The parallel that he derives between John 7:6 "Then Jesus said to them, "My time has not yet come, but your time is always ready." (NKJV) and the implication that this is the time of action is particularly clear as he declares that a revival of Christianity must take place. The world had already fallen away from the faith, now a resurgence of faith in the form of a Crusade must forcibly strengthen the Christianity so that when the End of Things inevitably appears, they will have done their duty by creating a greater number of Christians.
Guibert then provides a more extensive commendation for his people, recalling pre-Merovingian accomplishments:
"I say truly, and everyone should believe it, that God reserved this nation for such a task. For we know certainly that, from the time that they received the sign of faith that blessed Remigius brought to them, they succumbed to none of the diseases of false faith from which other nations have remained uncontaminated either with great difficulty or not at all. [...] Because it has carried the yoke since the days of its youth, it will sit in isolation, a nation noble, wise, war-like, generous, brilliant above all kinds of nations."
He consistently praises the Franks to the neglect of all others who participated in the Crusades. Even those that were not remotely Frankish, in particular Bohemund, were brought into the Frankish fold. For Guibert, the kind and noble actions of the Frankish nation when fighting the Gauls and dealing with the Spanish and Italians that wandered into their territory were proof that they were chosen by God to be Jerusalem's liberators. The tone of the memoirs that Guibert wrote remains consistently condemning and not confiding; they were written not by one searching for the true faith but by one determined to condemn the faithless and this condemnation included everyone who did not join in the fray or for that matter was a Frank. Guibert insists upon the providential nature of the accomplishments even going so far as to occasionally replacing the plural of Franks with the singular of God. In this way, Guibert lays the credit and responsibility for the deeds done, where they properly belong in both his mind and the prevailing attitude of the time period, in the infinite wisdom and experience of God.
He also makes it clear that the characters explicitly articulate their awareness of such providential responsibility. One of the major leaders of the Crusade, Bohemund, addresses his men:
"O finest knights, your frequent victories provide an explanation for your great boldness. Thus far you have fought for the faith against the infidel, and have emerged triumphant from every danger. Having already felt the abundant evidence of Christ's strength should give you pleasure, and should convince you beyond all doubt that in the most severe battles it is not you, but Christ, who has fought."
Even in this inspirational speech, Guibert reminds his audience that the person that is orchestrating the entire march for Jerusalem is God and that to him alone credit is due. He used grandiose writing to magnify the internal, psychological significance of the events, while simultaneously insisting upon the religious nature of the expedition. As he put it "in our time God ordained holy wars so that the knightly order and the wandering crowd - who had previously been engaged in slaughtering each other like their pagan ancestors - could find a new way of earning salvation". Even the civil wars were evidently part of God's plan in Guibert's eyes.
For Guibert, the instigation, inspiration, and result of the First Crusade was guided and directed by God. He clearly demonstrates that for the 10th century person the morality of the ensuing war was not to be questioned by using biblical allusions and justifications.