Theologically, Christianity didn't have an idea of a holy war. Like, war might be just, but fighting wasn't something that got you into heaven. But pilgrimage to a holy shrine could help you out on that front, and Urban had the key insight to pitch the Crusade as a pilgrimage with a touch of warring on the side. I do the same thing to my kid every night. I'm not feeding you dinner featuring animal crackers, I'm feeding you animal crackers featuring dinner. Oh, it's time for the open letter? An open letter to animal crackers.