What is the point of instant travel? Why is it integral to the priest game?
Medieval priests whose primary concern was the priesthood still took up arms. It was not their primary function, but they did not stop being a priest; Adhemar le Puy did not stop being a Bishop and become Sir Adhemar while on Crusade.
And there is nothing stopping a Bishop of whatever religion you want from changing class to Warrior and joining his brethren on a Crusade. He just can't try to kill the peasants one minute, and try to convert them the next.
And before you say that it would have been historically accurate for him to have done so: tough beans. There are plenty of things that would have been historically accurate that we prevent you from doing for game balance reasons. Like, say, handing your buddy 100 gold coins while you're out on a long campaign and he forgot to bring enough to pay his unit.
