An affliction containing two white hairs that spread over the entire body:
An affliction on a person's body in which two white hairs grew, which was brought before the kohen and declared tamei, and the affliction was pronounced tzaraas - and afterward the affliction spread over his entire body: even though the two white hairs remain in place, "tahor" - the person becomes tahor. This ruling applies even according to Rabbi Yehoshua in the previous Mishnah, since here there already was tzaraas, and only afterward did the affliction spread over the entire body, so that the spreading itself is what brings about his purity.
An affliction that spread a little and afterward broke out over the entire body:
An affliction that spread somewhat in size, and the kohen declared it to be tzaraas, and afterward it spread over the entire body - this is nothing other than a further spreading of that same tzaraas. In this case too "tahor", the person becomes tahor, because in the interim the affliction was declared tzaraas, and it is this tzaraas that spread over the entire body, and therefore he becomes tahor like any tzaraas that breaks out over the whole body.
An affliction that receded and disappeared from part of the body:
The Mishnah now repeats one of the rulings taught in the first Mishnah: in all these cases, where the person became tahor after the affliction spread over his entire body - once the affliction recedes and disappears from part of the body, even if it disappears only from the tip of a limb. Ordinarily, a patch of healthy skin in such a place on the body does not cause the affliction to be considered tzaraas, but here we learn from the verses that it counts like any area of healthy skin that renders the affliction tzaraas. Therefore the person becomes "tamei", and the affliction is tamei as tzaraas.
An affliction that spread over most of the body only:
The Mishnah concludes with an affliction that has already been established as tzaraas, the kohen having ruled that it is tzaraas, and it spreads over only part of the body. The Mishnah comes to teach that even if it spread over most of the body, its status is not that of an affliction that has broken out over all of it. In many areas of Torah law we find the principle that the majority of a thing is treated as significant as the whole of it, as though it were one hundred percent, and one might have thought that once most of the body is covered with the affliction it is as if all of it were covered, and the person would be tahor. The Mishnah teaches us that this is not so; rather, "tamei" - he remains in his tumah and the tzaraas is still considered tzaraas; and only if it spread over the entire body - "tahor", only then does the person become tahor.
In summary: in this Mishnah we learned four rulings: an affliction that was declared tzaraas, containing two white hairs, that spread over the entire body - tahor, even though the hairs remain in place; an affliction that spread a little, was declared tzaraas, and afterward spread over the entire body - tahor; an affliction that broke out over the entire body and then receded and disappeared from part of it, even from the tip of a limb - tamei; and an affliction that spread over most of the body only - tamei, for here we do not say that the majority is like the whole, and only spreading over the entire body brings purity.