That's a good question Joan!I'll hazard a guess, but bear in mind I've not seen these in person.
The text tells us that these shoes were used in a decidedly non-everyday manner, and that they're huge for the time. It suggests that the ends of the shoes (not very pointy) were probably stuffed to fill out the shape.
Perhaps the priest used these as overshoes when approaching the altar? If that were the case, the huge size would necessary to accomodate his normal shoes. I've studied alot of medieval liturgical practices, but not run across mention of special shoes.
The leather straps are strange. I think they are tied together that way for storage, not for use. I imagine they flopped down and perhaps a cord was tied around the ankle to keep them in place. This is pure speculation on my part.
Any one have any thoughts?
D