OK, then we’re talking about the First Crusade (1096-1099). That’s good. This is the only one of the eight Crusades that many apologists here care to defend. This was the “good Crusade.”
Eastern Christian lands had been conquered by Muslim forces and Islam imposed upon the population. The Byzantine Emperor appealed to Western Catholics volunteers to liberate his lands from these foreign invaders, especially the Holy City of Jerusalem (which is exactly what they did).
Pope Urban-2 saw this as a righteous cause and supported it. I don’t see how anyone (except maybe disgruntled Muslims) could disagree.
Was what they quoted the pope as saying really accurate?
The bit about the vile invaders is probably accurate (or surely something very similar was said). But the Pope never gave a preemptive pardon for any and all future sins. HOWEVER…
The second thing is how would I explain the indulgence that was given? Is this more like confession and penance? Did the pope even actually grant this to crusaders?
Crusaders were granted an indulgence, but for past sins, not for future sins. But future sins could still be forgiven…
The Crusade was considered a Holy War, waged for God against God’s enemies, so dying in this war meant dying a martyr’s death.
I don’t know if the implications of a martyr’s death have been formally defined by the Church (and I don’t believe they have), but it is an ancient and common pious belief that a martyr’s death restores our Baptismal Grace, should it have been lost (just as the Church teaches that a martyr’s death confers Baptismal Grace upon those who are not saved). We see evidence for this “martyr’s redemption” in the Scriptures:
Whoever finds his life will loose it, and whoever looses his life for my sake will find it [Matt 10:39]
Whoever wishes to save his life will lose it, but whoever looses his life for my sake will find it. [Matt 16:25]
He that hands over his life in this world will keep it unto life eternal. [John 12:25]
And we also see that the Church “relaxes the requirements” for Confession in cases of extreme necessity (CCC 1483).
If restoration of Baptismal Grace at the time of our death assures our salvation then a Crusader who committed any number and type of sins while marching to Jerusalem would be absolved if he was killed in the cause of Christ.
The Pope certainly did not encourage bad behavior, but the Crusaders weren’t stupid, and they understood the implications of their martyrdom. Some of them surely figured they could pretty much do whatever they wanted and yet be saved if they were killed (and, if they survived, they could always attend Confession).
It’s really no different than a mortally wounded (but still living) Crusader calling for a priest and making his Confession before he dies. No matter how much raping and pillaging he had done during the march, he would be saved.