Such exemptions create a significant benefit to Christianity in general because it creates a sort of reverse taxation on paganism: not only do Christians have to pay less as Roman citizens, but pagans have to pay more to make up for what Christian clergy don't pay.
This new Roman law states:
"No class of men, by merit of any high rank or veneration, shall be exempt from the construction and repair of roads and bridges. We also gladly ascribe the property of the divine imperial household and the venerable churches to such a laudable list." [CTh 15.3.6]