Imagine a disease that affects the walls of your house.
It looks like a bad case of mildew, but the Torah considers it to be of real concern.
The house must be inspected by a kohen and in extreme cases the house must be evacuated for a specific duration.
In the most extreme cases the house must be destroyed.
But by finely interpreting the exact wording of the Torah, our sages discover that there may be a silver lining to the household disaster.