Apparently it was required, to make sure the woman was a virgin and that the prince was the father.

Still, after a long line of descriptions of how wonderful the wedding was, the poet eagerly telling us that there were lots and lots and lots of clergymen at the deflowering is particularly hilarious.

I mean, Chrétien is trying to emphasize that the king spared no expense by telling us there wasn't just one local priest there on the wedding night, but a whole stable's worth of high clergy.