Order in the Court!
Remember back in Sefer Shemos (Chapter 4, Pasuk 23), HaShem instructed Moshe at the burning bush to warn Paraoh to let the Jews free? The instructions were specific. He was to tell Paraoh about the last of the 10 plagues: “If you don’t let the Jews free HaShem will kill all the first-born Egyptians!
Why wasn’t Moshe told to warn Pharaoh about the other 9 plagues?!
Well, when you want to threaten, you go straight to the most severe plague, and that was no doubt the death of the first-born.
Similarly, the Torah here starts with the most severe punishment – first Tsara’as on a person’s skin; then the closest thing to a person – Tsara’as on the clothes; and finally something further away – Tsara’as on the house.
But HaShem is truly compassionate, and when the Tsara’as punishment came to the person, it was the exact opposite, just as the Rambam here described – house Tsara’as, clothes Tsara’as, and when a person still didn’t do Teshuvah then came… Tsara’as on the skin… OUCH!